A145837 - OEIS

%I #11 Sep 08 2018 17:45:42

%S 3,8,11,15,20,23,36,44,47,48,60,68,71,75,83,84,87,92,111,116,128,132,

%T 143,144,156,159,164,167,168,183,192,200,204,207,215,224,228,231,236,

%U 239,264,272,287,299,300,303,312,315,320,323,356,359,360,363,372,387

%N Indices of primes in A005891(n).

%C Corresponding centered pentagonal primes are listed in A145838 = {31, 181, 331, 601, 1051, 1381, 3331, ...}.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/CenteredPentagonalNumber.html">Centered Pentagonal Number</a>

%F A005891(a(n)) = A145838(n)

%t (Position[LinearRecurrence[{3,-3,1},{1,6,16},400], _?PrimeQ]// Flatten)-1 (* _Harvey P. Dale_, Sep 08 2018 *)

%Y Cf. A145838 = Primes in A005891. Cf. A005891 = Centered pentagonal numbers: (5n^2+5n+2)/2.

%K nonn

%O 1,1

%A _Alexander Adamchuk_, Mar 21 2009

%E Extended by _R. J. Mathar_, Mar 26 2009

%E Edited by _N. J. A. Sloane_, Apr 06 2009