

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
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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

JuriStepan 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



