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A173474 Numbers n such that n*2^n + 1 is not prime. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 17 10:08 EST 2019. Contains 319218 sequences. (Running on oeis4.)