20101201, 04:01  #1 
Aug 2004
New Zealand
DB_{16} Posts 
Numbers wanted for OEIS sequences
The OEIS has a number of sequences needing more terms but which are currently blocked on finding factors of various numbers. In some cases, it would suffice to find a single factor, in other cases complete factorization is required. This list should not be considered exhaustive.
A046461 Is Smarandache(691) a semiprime. A063684 Factorization of 105!+2. A078781 Is 151!1 a semiprime. A080802 Is 151!1 a semiprime. A081715 Is 3^514+2 a semiprime. A085745 Is 2^1239+1239 a semiprime. A085747 Is 90!+97 a semiprime. A099954 Is Fibonacci(1801) a semiprime. A115101 Factorization of Lucas(2602). A115973 Factorization of 101^101+1 A165767 Is 2^669669 a semiprime. A167937 Is 114!+1 a semiprime. 
20101201, 06:39  #3 
Mar 2006
Germany
2×1,423 Posts 
Here's another one:
EuclidMullinSequence: A000945 and an overview here (needs first factor of a C256 of index 47). Or the smallest open Sequence of Home Prime Base 10 for n=49 (Factorization of index 103 of C178). 
20101201, 13:35  #4  
Nov 2003
16444_{8} Posts 
Quote:
Some of the numbers mentioned above are well within current capabilities. Some are just out of reach (e.g. 2^1239 + 1239, 151!1). Some are well beyond them. (e.g. F1801, L2602) 

20101201, 14:17  #5 
Aug 2006
3·5^{2}·79 Posts 
It's selection bias: detecting semiprimes requires factorization of a 'pure' composite, and this thread is looking for sequences requiring hard factorizations. Similarly, to be large enough to be difficult but also small enough to be doable, most of these sequences have exponential growth; that's also an artifact of our selection, since most OEIS sequences don't share that feature.

20101210, 19:21  #6 
Aug 2006
3·5^{2}·79 Posts 
Also someone might consider submitting a bfile for sequences such as
http://oeis.org/A078604 
20101211, 17:03  #7  
"Forget I exist"
Jul 2009
Dumbassville
2^{6}·131 Posts 
Quote:


20101211, 17:24  #8  
"Forget I exist"
Jul 2009
Dumbassville
2^{6}·131 Posts 
Quote:
Code:
if([isprime(factor(6)),1] && !isprime(6) ,print(factor(6))) 

20101211, 17:26  #9  
"Forget I exist"
Jul 2009
Dumbassville
2^{6}·131 Posts 
Quote:


20101211, 17:38  #10 
"Forget I exist"
Jul 2009
Dumbassville
2^{6}×131 Posts 
never mind the [] gives a fault anyways.
Code:
checking(y)= c="";for(z=1,y,c=concat(c,z));if(!isprime(eval(c)) ,print(y)) Last fiddled with by science_man_88 on 20101211 at 18:07 
20101211, 18:33  #11 
"Forget I exist"
Jul 2009
Dumbassville
2^{6}·131 Posts 
http://oeis.org/A006881 has a small error in the PARI code ( a missing semicolon) I know this because i was thinking of going off this next, and then just using eval(c) in the place of n and checking if a integer sqrt was present I do that and we have a code for http://oeis.org/A046461 as well.

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