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 A081641 #11 Nov 18 2024 12:18:56
%S A081641 36449279,53065907,59681213,69096887,132756479,135388367,164255999,
%T A081641 179043637,188991053,207290663,241560239,279709259,309550999,
%U A081641 364492781,372993983,377982103,398007431,406165099,425633717,445901987,447609067,516737983
%N A081641 a(n) = n-th prime of class 13- according to the Erdős-Selfridge classification.
%D A081641 R. K. Guy, Unsolved Problems in Number Theory, A18.
%H A081641 M. F. Hasler, <a href="/A081641/b081641.txt">Table of n, a(n) for n=1..1641</a>
%t A081641 PrimeFactors[n_Integer] := Flatten[ Table[ #[[1]], {1}] & /@ FactorInteger[n]]; f[n_Integer] := Block[{m = n}, If[m == 0, m = 1, While[ IntegerQ[m/2], m /= 2]; While[ IntegerQ[m/3], m /= 3]]; Apply[Times, PrimeFactors[m] - 1]]; ClassMinusNbr[n_] := Length[ NestWhileList[f, n, UnsameQ, All]] - 3; Prime[ Select[ Range[23733333], ClassMinusNbr[ Prime[ # ]] == 12 &]]
%o A081641 (PARI) A081641 = nextclassminus(A081640) /* cf. A081640 - _M. F. Hasler_, Apr 05 2007 */
%Y A081641 Cf. A005113, A005105, A005106, A005107, A005108, A081633, A081633, A081635, A081636, A081637, A081638.
%Y A081641 Cf. A056637, A081640, A129248.
%K A081641 nonn
%O A081641 1,1
%A A081641 _Robert G. Wilson v_, Mar 23 2003
%E A081641 Edited by _N. J. A. Sloane_, May 14 2008 at the suggestion of R. J. Mathar.