Can someone factor 2^61-1 for me?

[chuckywang]

GOT IT!

It's prime.

 

[cheezmunky]

2305843009213693951?

that has to be too easy

 

[KLin]

2305843009213690000

maybe 42


EDIT: could be 1152921504606850000

 

[chuckywang]

Originally posted by: cheezmunky
2305843009213693951?

that has to be too easy

Then what is it?

 

[chuckywang]

Originally posted by: KLin
2305843009213690000

maybe 42


EDIT: could be 1152921504606850000

Uh...2^61-1 is not divisible by 2.

 

[Tylanner]

.999999999999999999

 

[Jmmsbnd007]

2305843009213693951
according to windows calc

 

[cheezmunky]

Originally posted by: chuckywang

Then what is it?

according to the ti-89 it is 2305843009213693951 but I thought you might have wanted to expand it into a form with a bunch of products or soemthing

 

[chuckywang]

Originally posted by: Jmmsbnd007
2305843009213693951
according to windows calc

i want it factored (as in prime factorization), not as a decimal.

 

[beer]

MATLAB gives me a middle finder

 

[chuckywang]

Originally posted by: beer
MATLAB gives me a middle finder

Exactly.

 

[chuckywang]

N/m. I got it. It's prime.

 

[her209]

2^0 = 1
2^1 = 10
2^2 = 100
2^3 = 1000
...
2^61 = 1000...0 (61 zeros)

(2^61)-1 = 1111...1 (60 ones)

Does that help any?

 

[Jmmsbnd007]

Originally posted by: chuckywang

Originally posted by: Jmmsbnd007
2305843009213693951
according to windows calc

i want it factored (as in prime factorization), not as a decimal.

no you don't

 

[BigPoppa]

Originally posted by: her209
2^0 = 1
2^1 = 10
2^2 = 100
2^3 = 1000
...
2^61 = 1000...0 (61 zeros)

(2^61)-1 = 1111...1 (60 ones)

Does that help any?

Ummm:
2^0 does in fact = 1.
2^1 = 2
2^2 = 4
2^3 = 8
2^4 = 16

and so on. I have no clue what you think you were doing

 

[RaynorWolfcastle]

2^61-1 is prime according to Maple


edit: Guess I could have refreshed, I thought there was something I was missing when you were looking for factors and Maple was saying that it's prime... It's a Mersenne Prime btw. the kind that Prime95 finds

 

[JohnCU]

Originally posted by: BigPoppa

Originally posted by: her209
2^0 = 1
2^1 = 10
2^2 = 100
2^3 = 1000
...
2^61 = 1000...0 (61 zeros)

(2^61)-1 = 1111...1 (60 ones)

Does that help any?

Ummm:
2^0 does in fact = 1.
2^1 = 2
2^2 = 4
2^3 = 8
2^4 = 16

and so on. I have no clue what you think you were doing

he's doing binary.

 

[statik213]

Originally posted by: her209
2^0 = 1
2^1 = 10
2^2 = 100
2^3 = 1000
...
2^61 = 1000...0 (61 zeros)

(2^61)-1 = 1111...1 (60 ones)

Does that help any?

lol

 

[beer]

Originally posted by: chuckywang

Originally posted by: beer
MATLAB gives me a middle finder

Exactly.

I looked into the underlying code to figure out why. I read the comments and they said they chose to error-out if n > 2^32 due to large memory consumption. Thinking I was a badass, I removed the error checking in factor.m and executed the code - the underying reason matlab won't do it is that the function primes.m creates a vector 1:2, and that vector op - and for that matter, every vector op in matlab - seems to peg an upper bound at 2^32 elements

 

[illusion88]

Originally posted by: Tylanner
.999999999999999999...=1

 

[RaynorWolfcastle]

Originally posted by: beer

Originally posted by: chuckywang

Originally posted by: beer
MATLAB gives me a middle finder

Exactly.

I looked into the underlying code to figure out why. I read the comments and they said they chose to error-out if n > 2^32 due to large memory consumption. Thinking I was a badass, I removed the error checking in factor.m and executed the code - the underying reason matlab won't do it is that the function primes.m creates a vector 1:2, and that vector op - and for that matter, every vector op in matlab - seems to peg an upper bound at 2^32 elements

probably because integers larger than 32-bits are a mess to deal with on x86 and require you to make a new underlying datatype to get around the fact that there's no longlong datatype.

 

[So]

Originally posted by: beer

Originally posted by: chuckywang

Originally posted by: beer
MATLAB gives me a middle finder

Exactly.

I looked into the underlying code to figure out why. I read the comments and they said they chose to error-out if n > 2^32 due to large memory consumption. Thinking I was a badass, I removed the error checking in factor.m and executed the code - the underying reason matlab won't do it is that the function primes.m creates a vector 1:2, and that vector op - and for that matter, every vector op in matlab - seems to peg an upper bound at 2^32 elements

Impressive. :thumbsup::thumbsup:

 

[beer]

Originally posted by: RaynorWolfcastle

Originally posted by: beer

Originally posted by: chuckywang

Originally posted by: beer
MATLAB gives me a middle finder

Exactly.

I looked into the underlying code to figure out why. I read the comments and they said they chose to error-out if n > 2^32 due to large memory consumption. Thinking I was a badass, I removed the error checking in factor.m and executed the code - the underying reason matlab won't do it is that the function primes.m creates a vector 1:2, and that vector op - and for that matter, every vector op in matlab - seems to peg an upper bound at 2^32 elements

probably because integers larger than 32-bits are a mess to deal with on x86 and require you to make a new underlying datatype to get around the fact that there's no longlong datatype.

That is a good point. MATLAB treats every data type as a default double, though. I'm wondering if it does the calculations using a double-precision floating point op? If it does, it explains why it is so slow- the integer functional units on P4s are 2x core clock speed, so mine would be 6 GHz, if I recall - floating point would operate at regular clock speed but I'd imagine the memory bandwidth issue would be the limiting factor, not the core speeds. Trying to factor a number in the range of 2^60 involves a hell of a lot of swapping, and a swap operation can take hundreds of thousands of cycles (~milliseconds) compared to tens of nanoseconds for a floating point op.

 

[EpsiIon]

Originally posted by: BigPoppa

Originally posted by: her209
2^0 = 1
2^1 = 10
2^2 = 100
2^3 = 1000
...
2^61 = 1000...0 (61 zeros)

(2^61)-1 = 1111...1 (60 ones)

Does that help any?

Ummm:
2^0 does in fact = 1.
2^1 = 2
2^2 = 4
2^3 = 8
2^4 = 16

and so on. I have no clue what you think you were doing

There are 10 types of people in the world: those who know binary and those who don't.

 

[Jassi]

Originally posted by: JohnCU

Originally posted by: BigPoppa

Originally posted by: her209
2^0 = 1
2^1 = 10
2^2 = 100
2^3 = 1000
...
2^61 = 1000...0 (61 zeros)

(2^61)-1 = 1111...1 (60 ones)

Does that help any?

Ummm:
2^0 does in fact = 1.
2^1 = 2
2^2 = 4
2^3 = 8
2^4 = 16

and so on. I have no clue what you think you were doing

he's doing binary.

pwned!