A173474 Numbers n such that n*2^n + 1 is not prime.

0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72

Offset

1,2

Comments

Complement of "prime Cullen numbers" A005849.

Where a(n)=n for n <= 140, and a(141)=142,..., a(4711)=4712, a(4712)=4714,..., a(5792)=5794, a(5793)=5796,..., a(6607)=6610, a(6608)=6612,..., a(18491)=18495, a(18492)=18497,..., a(32286)=32291, a(32287)=32293,..., a(32462)=32468, a(32463)=32470,..., a(59648)=59655, a(59649)=59657,..., a(90816)=90824, a(90817)=90826,..., a(262403)=262418, a(262404)=262420,..., a(361264)=361274, a(361265)=361276,..., a(481887)=481898, a(481888)=481900,..., a(1354815)=1354827, a(1354816)=1354829,..., a(6328534)=6328547, a(6328535)=6328549,...

Otherwise said, this includes all nonnegative integers except for the "prime Cullen numbers" (more precisely, indices of primes in A002064): 1, 140, 4713, 5795, ... listed in A005849. - M. F. Hasler, Jan 18 2015

Links

G. C. Greubel, Table of n, a(n) for n = 1..5000

Mathematica

nnnpQ[n_]:=Module[{c=n 2^n+1}, !PrimeQ[c]&&c>=0]; Select[Range[0, 100], nnnpQ] (* Harvey P. Dale, Aug 23 2011 *)

Crossrefs

Cf. A005849, A045344, A050920, A087156, A141468.

Sequence in context: A130446 A132086 A136602 * A023443 A099570 A114142

Adjacent sequences: A173471 A173472 A173473 * A173475 A173476 A173477

Keyword

nonn

Author

Juri-Stepan Gerasimov, Feb 19 2010

Extensions

Corrected and edited by M. F. Hasler, Jan 18 2015

Name edited by Michel Marcus, Nov 02 2017

Status

approved