Other Factordb Problems

[Batalov]

Originally Posted by axn

...and apparently PFGW's definition of ## is different from factordb's, so it is tagged as composite.

## in FactorDB seems to be known to be incorrect (and of course, any larger number of ##...#s, by extension)
Point in case: 4# is correctly parsed as 6, but then, why is 4## = 210 in FactorDB??

[Wick]

According to the help:

# Primordial (product of all primes below n, postfix)
## Product first n primes (postfix)

4# = 6
4## = 210 (2*3*5*7)
(4#)# = 30

seems correct?

[Batalov]

1) That's a very "intuitive" design. If you can show how to get this helpful "help"? except as deduced by this comment that it actually exists, and if so, then it just might be at factordb.com/help ... and in fact this page [B]does[/B] exist, in its own world - not linked to any other pages.
2) nobody uses this notation
3) what is 4### then? and why? and what is 4#### -- is it (4##)## ? (((4#)#)#)# ? ((4#)#)## ? ((4##)#)# ?

[axn]

FWIW, I just put n## in the search box and looked at the series that factordb printed out.

Of course, the problem is that PFGW interprets ## the same way it inteprets !! (multifactorials), i.e. product of every other prime.

What we've got here is failure to communicate

[Batalov]

Yes, the PFGW way makes sense. Using ## for something that cannot be written (easily) in another way makes more sense.
Like the motto of a certain method, “To make the impossible possible, the possible easy, and the easy elegant.”

Using n## for p_n# doesn't make impossible possible, or even possible much easier than it is. If 4## is simply 7# and 10## is simply 29#, then what's the economy?

[axn]

Originally Posted by Batalov

Using n## for p_n# doesn't make impossible possible, or even possible much easier than it is.

Not when we're looking at an individual number, no. But, it does help when looking at series. For example, I believe the two numbers I posted came out of series n##*2^n+/-1.

Anywho... whatever format it internally supports, it needs to standardise that when communicating with external tools (like PFGW).

PS:- From factordb.com home page, if you click on the ? link to the right, you'll get the help link. It has page=0 parameter. There are apparently help pages available for 1 & 2 as well

[Batalov]

True!

I saw a similar conceptual disconnect at UTM, but in a rare category. I submitted a partition number and all old submissions were in "p(n)" form. But for PFGW, p(n) is the prime number #n, so for a brief moment the prime was deleted (for being too small), then restored again manually by CC.

So, anyway, FactorDB's 10## could be represented as p(10)# in PFGW (and could as well be the same in factorDB, if a prefix function p(n) is implemented).

Let's see. PFGW has these built in: p(n), Phi(n,x), gcd(x,y), F(n), L(n), and also U(n), V(n) (primitive parts of F(n), L(n)); doesn't have numbpart(), or bernfrac(), or some other things, -- for them one can use a bridge from GP to PFGW. FactorDB has only a subset of these.

[Antonio]

Originally Posted by Wick

According to the help:

# Primordial (product of all primes below n, postfix)
## Product first n primes (postfix)

4# = 6
4## = 210 (2*3*5*7)
(4#)# = 30

seems correct?

Factordb is still inconsistent even with it's own definition.
Consider it's solution to 5# =2*3*5 =30, which should be the same as 4# according to it's definition..

[Wick]

Originally Posted by Batalov

1) That's a very "intuitive" design. If you can show how to get this helpful "help"? except as deduced by this comment that it actually exists, and if so, then it just might be at factordb.com/help ... and in fact this page [B]does[/B] exist, in its own world - not linked to any other pages.
2) nobody uses this notation
3) what is 4### then? and why? and what is 4#### -- is it (4##)## ? (((4#)#)#)# ? ((4#)#)## ? ((4##)#)# ?

next to the factorize button on every page there is a ?. If you click it you go here: http://www.factordb.com/help.php?page=0

[chris2be8]

Factordb seems unreasonably slow processing primorials. Eg the following two PRPs should be easy to prove prime by N-1 but clicking on Primality gets a LONG wait then an incomplete page as if the attempt to calculate how far factored N-1 is timed out.

26901*115637#+1
27545*115637#+1

Chris

[Stargate38]

What's causing the "err" status on certain numbers? It's breaking 9 of the Aliquot sequences. Here's an example (from 270870):

http://factordb.com/index.php?id=1100000000626093582