A193066 - OEIS

%I #11 Sep 24 2016 17:56:13

%S 3,5,17,27,39,41,49,59,71,89,101,125,131,167,169,173,289,293,383,507,

%T 529,677,701,729,743,761,773,827,839,841,857,911,1091,1097,1163,1181,

%U 1193,1217,1373,1427,1487

%N Odd numbers N such that numerator(sigma(N^2)/N^2) is a prime.

%C Square roots of the terms of A193065. See there for more comments.

%H Harvey P. Dale, <a href="/A193066/b193066.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = A000196(A193065(n)).

%t Select[Range[1,1501,2],PrimeQ[Numerator[DivisorSigma[1,#^2]/#^2]]&] (* _Harvey P. Dale_, Sep 24 2016 *)

%o (PARI) forstep(N=1, 1e7, 2, isprime(numerator(sigma(N^2)/N^2)) && print1(N", "))

%K nonn

%O 1,1

%A _M. F. Hasler_, Jul 15 2011