This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A193070 #17 Jan 22 2019 17:30:07 %S A193070 3,5,17,27,41,49,59,71,89,101,125,131,167,169,173,289,293,383,529,677, %T A193070 701,729,743,761,773,827,839,841,857,911,1091,1097,1163,1181,1193, %U A193070 1217,1373,1427,1487,1559,1583,1709,1811,1847,1849,1931,1973,2129,2197,2273,2309 %N A193070 Odd numbers N for which sigma(N^2) is prime. %C A193070 The function sigma(n) (=A000203(n)) takes odd values when n is a square or twice a square. Thus, odd numbers n for which sigma(n) is prime (i.e. which are in A023194) must be odd squares. This sequence consists exactly of the square roots of these terms. %H A193070 T. D. Noe, <a href="/A193070/b193070.txt">Table of n, a(n) for n = 1..10000</a> %F A193070 a(n) = A278911(n)^(1/2). - _Robert Israel_, Jan 22 2019 %t A193070 Select[Range[1,2401,2],PrimeQ[DivisorSigma[1,#^2]]&] (* _Harvey P. Dale_, Mar 07 2015 *) %o A193070 (PARI) forstep(N=1, 1e7, 2, isprime(sigma(N^2)) && print1(N", ")) %Y A193070 Cf. A000203, A023194, A195382, A278911. %K A193070 nonn %O A193070 1,1 %A A193070 _M. F. Hasler_, Jul 15 2011