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 A292238 #4 Sep 12 2017 12:32:43 %S A292238 2,3,5,7,11,13,257,73,23,29,331,37,163,43,47,53,61,1321,2677,1609,73, %T A292238 79,83,2931542417,97,278557,599,28059810762433,31981,113,77158673929, %U A292238 131,27977333,457,37888318897441,151,4523,461,541,173,179,181,191,587,197,3690437 %N A292238 a(n) = gpf(lpf(2^prime(n) - 1) - 1) where prime(n) is the n-th prime. %F A292238 For p in A291691, let pp be such that p = prime(pp), then a(pp) = p. %o A292238 (PARI) a(n) = vecmax(factor(vecmax(factor(2^prime(n)-1)[, 1])-1)[, 1]); %Y A292238 Cf. A001348, A291691, A292237. %K A292238 nonn %O A292238 1,1 %A A292238 _Michel Marcus_, Sep 12 2017