Search: id:A056561
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%I A056561
%S A056561 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,
%T A056561 26,27,28,29,30,31,32,33,34,35,36,37,38,39,42,43,45,46,47,48,50,51,52,
%U A056561 53,54,55,57,58,59,60,61,62,63,64,66,67,68,69,70,71,72,73,74,75,77,78
%N A056561 Numbers n such that n^2 + n + 41 is prime.
%C A056561 Among first 100000 terms, the only run of 13 subsequent values >39 is 
               219..231. [From Zak Seidov (zakseidov(AT)yahoo.com), Jan 28 2009]
%D A056561 P. Hoffman, Archimedes' Revenge, pp. 39-40,Penguin Books 1988.
%H A056561 Zak Seidov, <a href="b056561.txt">Table of n, a(n) for n = 1..10000.</
               a>
%F A056561 a(n) =(sqrt(4*A005846(n)-163)-1)/2
%e A056561 39 is in the sequence because 39^2+39+41=1601 which is prime but 40 is 
               not because 40^2+40+41=1681=41*41
%Y A056561 Cf. A002837, A005846, A007634.
%Y A056561 Sequence in context: A044923 A083243 A002837 this_sequence A085735 A044922 
               A132145
%Y A056561 Adjacent sequences: A056558 A056559 A056560 this_sequence A056562 A056563 
               A056564
%K A056561 nonn
%O A056561 1,3
%A A056561 Henry Bottomley (se16(AT)btinternet.com), Jun 26 2000

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