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

%I A173474 #21 Nov 02 2017 09:13:44
%S A173474 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,
%T A173474 27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,
%U A173474 50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72
%N A173474 Numbers n such that n*2^n + 1 is not prime.
%C A173474 Complement of "prime Cullen numbers" A005849.
%C A173474 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,...
%C A173474 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
%H A173474 G. C. Greubel, <a href="/A173474/b173474.txt">Table of n, a(n) for n = 1..5000</a>
%t A173474 nnnpQ[n_]:=Module[{c=n 2^n+1},!PrimeQ[c]&&c>=0]; Select[Range[0,100], nnnpQ] (* _Harvey P. Dale_, Aug 23 2011 *)
%Y A173474 Cf. A005849, A045344, A050920, A087156, A141468.
%K A173474 nonn
%O A173474 1,2
%A A173474 _Juri-Stepan Gerasimov_, Feb 19 2010
%E A173474 Corrected and edited by _M. F. Hasler_, Jan 18 2015
%E A173474 Name edited by _Michel Marcus_, Nov 02 2017