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 A123751 #13 Feb 16 2025 08:33:03
%S A123751 5,266681,40799043101,86364397717734821,
%T A123751 36190908596780862323291147613117849902036356128879432564211412588793094572280300268379995976006474252029,
%U A123751 334279880945246012373031736295774418479420559664800307123320901500922509788908032831003901108510816091067151027837158805812525361841612048446489305085140033
%N A123751 Primes in A007406.
%C A123751 A007406 lists the Wolstenholme numbers.
%C A123751 Numbers k such that A007406(k) is prime are listed in A111354.
%H A123751 Carlos M. da Fonseca, M. Lawrence Glasser, Victor Kowalenko, <a href="https://doi.org/10.2298/AADM1801070F">Generalized cosecant numbers and trigonometric inverse power sums</a>, Applicable Analysis and Discrete Mathematics, Vol. 12, No. 1 (2018), 70-109.
%H A123751 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HarmonicNumber.html">Harmonic Number</a>.
%H A123751 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/WolstenholmesTheorem.html">Wolstenholme's Theorem</a>.
%H A123751 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/WolstenholmeNumber.html">Wolstenholme Number</a>
%F A123751 a(n) = A007406(A111354(n)).
%e A123751 A007406 begins {1, 5, 49, 205, 5269, 5369, 266681, 1077749, 9778141, ...}.
%e A123751 Thus a(1) = 5 because A007406(2) = 5 is prime but A007406(1) = 1 is not prime.
%e A123751 a(2) = 266681 because A007406(7) = 266681 is prime but all A007406(k) are composite for 2 < k < 7.
%t A123751 Do[f=Numerator[Sum[1/i^2,{i,1,n}]]; If[PrimeQ[f],Print[{n,f}]],{n,1,250}]
%Y A123751 Cf. A111354, A007406, A001008, A007407, A067567, A056903.
%K A123751 nonn
%O A123751 1,1
%A A123751 _Alexander Adamchuk_, Oct 11 2006