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a(n) = 1 + 4*A034780(n).
1

%I #12 May 14 2018 20:24:38

%S 29,53,101,109,149,173,181,197,229,269,293,317,337,349,373,389,461,

%T 509,557,569,641,653,677,701,709,773,797,821,829,853,937,941,1013,

%U 1021,1033,1061,1069,1109,1117,1181,1193,1217,1229,1277,1297,1301,1373,1429,1481,1493,1549,1597

%N a(n) = 1 + 4*A034780(n).

%C a(n) = P(n,4) = 1 + 4*K(n,4) = 1 + 4*A034780(n). P(n,4) are special primes of the form 4k+1. The relevant values of k are given by A034780.

%C Note that, e.g., 5 and 13 are not in this sequence.

%o (PARI) a034693(n) = my(s=1); while(!isprime(s*n+1), s++); s;

%o isok(n) = a034693(n) == 4;

%o lista(nn) = {for (n=1, nn, if (isok(n), print1(4*n+1, ", ")););} \\ _Michel Marcus_, May 13 2018

%Y Cf. A034693, A034694, A034780.

%K nonn

%O 1,1

%A _Labos Elemer_

%E More terms from _Michel Marcus_, May 13 2018