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%I #17 Jul 10 2015 19:23:08
%S 3,5,11,31,41,23,73,131,47,97,149,83,229,167,89,337,311,167,307,293,
%T 149,499,509,211,457,509,311,607,743,211,787,839,331,877,521,419,1171,
%U 911,421,787,1289,419,1279,1103,433,1327,1361,619,1123,1103,617,1663,1721,661,1039,1553,739,2179,2111,599
%N a(n) is the n-th smallest prime p such that p+4n is also prime.
%C There is an array defined by: A(n,k) is the k-th smallest prime such that p+4*n is also prime (analog of A231608). It starts
%C 3 7 13 19 37 43 67 79 97 103
%C 3 5 11 23 29 53 59 71 89 101
%C 5 7 11 17 19 29 31 41 47 59
%C 3 7 13 31 37 43 67 73 97 151
%C 3 11 17 23 41 47 53 59 83 89
%C 5 7 13 17 19 23 29 37 43 47
%C 3 13 19 31 43 61 73 79 103 109
%C 5 11 29 41 47 71 107 131 149 167
%C 5 7 11 17 23 31 37 43 47 53
%C 3 7 13 19 31 43 61 67 73 97
%C a(n) = A(n,n) reads along the main diagonal of this array. - _R. J. Mathar_, Nov 19 2014
%H Zak Seidov, <a href="/A246901/b246901.txt">Table of n, a(n) for n = 1..1000</a>
%o (PARI) a(n) = nb=0; forprime(p=3,, if (isprime(p+4*n), nb++; if (nb==n, return (p)))); \\ _Michel Marcus_, Nov 16 2014
%Y Cf. A086505.
%K nonn
%O 1,1
%A _Zak Seidov_, Nov 16 2014