The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A253178 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
Showing entries 1-10 | older changes

A253178

Least k>=1 such that 2*A007494(n)^k+1 is prime.
(history; published version)

#58 by Bruno Berselli at Mon Apr 13 05:10:50 EDT 2015

STATUS

proposed

approved

#57 by Joerg Arndt at Mon Apr 13 05:03:16 EDT 2015

STATUS

editing

proposed

#56 by Joerg Arndt at Mon Apr 13 05:02:47 EDT 2015

COMMENTS

a(145) > 200000, a(146) - .. a(156) = {1, 1, 66, 1, 4, 3, 1, 1, 1, 1, 6}, a(157) > 100000, a(158) - .. a(180) = {2, 1, 2, 11, 1, 1, 3, 321, 1, 1, 3, 1, 2, 12183, 5, 1, 1, 957, 2, 3, 16, 3, 1}.

PROG

(PARI) a007494(n) = n+(n+1)>>1;

a(n) = for(k=1, 2^24, if(ispseudoprime(2*a007494(n)^k+1), return(k)));

STATUS

proposed

editing

Discussion

Mon Apr 13

05:03

Joerg Arndt: Looks OK to me now.

#55 by Eric Chen at Fri Apr 10 04:05:13 EDT 2015

STATUS

editing

proposed

#54 by Eric Chen at Fri Apr 10 04:04:49 EDT 2015

CROSSREFS

Cf. A138066, A138067, A255707, A250200, A119624, A119591, A040076, A046067.

STATUS

proposed

editing

Discussion

Fri Apr 10

04:05

Eric Chen: Is there any base such that 2 is a Sierpinski number?

#53 by Eric Chen at Tue Apr 07 10:52:35 EDT 2015

STATUS

editing

proposed

#52 by Eric Chen at Tue Apr 07 10:52:09 EDT 2015

COMMENTS

If n == 1 (mod 3), then for every positive integer k, 2*n^k+1 is divisible by 3 and cannot be prime (unless n=1). Thus we restrict the domain of this sequence to A007494. (n which is not in the form 3j+1).

Discussion

Tue Apr 07

10:52

Eric Chen: I changed.

#51 by Eric Chen at Tue Apr 07 10:51:38 EDT 2015

COMMENTS

If n ==3j+ 1, (mod 3), then all for every positive integer k, 2*n^k+1 are is divisible by 3 and cannot be prime, so (unless n=1). Thus we limited restrict the n in domain of this sequence to A007494 . (n which is not in the form 3j+1).

#50 by Danny Rorabaugh at Mon Apr 06 12:43:02 EDT 2015

STATUS

proposed

editing

#49 by Eric Chen at Wed Apr 01 06:51:29 EDT 2015

STATUS

editing

proposed

Discussion

Wed Apr 01

23:13

Jon E. Schoenfield: @Eric -- << You approved A119624, why not approve this sequence? >>

Why not reword the 2nd half of the first sentence in the Comments so that it says what you really mean for it to say?  As it is, what it says is incorrect.  I think Michel's Mar 25 comment suggests a much better wording.

Mon Apr 06

12:43

Danny Rorabaugh: My two cents: "If n == 1 (mod 3), then for every positive integer k, 2*n^k+1 is divisible by 3 and cannot be prime (unless n=1). Thus we restrict the domain of this sequence to A007494."