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 A136681 #21 Feb 16 2025 08:33:07
%S A136681 3,4,5,6,9,10,13,16,17,18,37,43,58,121,124,126,137,203,247,283,285,
%T A136681 286,289,317,424,508,751,790,937,958,1066,1097,1151,1166,1194,1199,
%U A136681 1235,1414,1418,1460,1498,1573,2090,2122,2691,2718,3030,3426,3600,3653,3737
%N A136681 Numbers k such that A058313(k) is prime.
%C A136681 A058313(k) = Numerator of Sum_{j=1..k} (-1)^(j+1)/j.
%H A136681 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HarmonicNumber.html">Harmonic Number</a>
%t A136681 Do[ f=Numerator[ Sum[ (-1)^(k+1)*1/k, {k,1,n} ] ]; If[ PrimeQ[f], Print[ {n,f} ] ], {n,1,317} ]
%o A136681 (PARI) isok(n) = isprime(numerator(sum(k=1, n, (-1)^(k+1)/k))); \\ _Michel Marcus_, Mar 14 2019
%Y A136681 Cf. A058313, A119682, A120296, A136675, A136676, A136677.
%Y A136681 Cf. A001008, A007406, A007408, A007410, A099828, A103345.
%Y A136681 Cf. A136682, A136683, A136684, A136685, A136686.
%K A136681 nonn
%O A136681 1,1
%A A136681 _Alexander Adamchuk_, Jan 16 2008
%E A136681 a(25)-a(30) from _James R. Buddenhagen_, Sep 22 2015
%E A136681 a(31)-a(51) from _Amiram Eldar_, Mar 14 2019