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 A023511 #13 Jun 06 2019 02:44:02 %S A023511 3,1,3,1,3,7,3,5,3,3,1,19,3,11,3,3,3,31,17,3,37,5,3,3,7,3,13,3,5,3,1, %T A023511 3,3,5,3,19,79,41,3,3,3,7,3,97,3,5,53,7,3,5,3,3,11,3,3,3,3,17,139,3, %U A023511 71,3,7,3,157,3,83,13,3,5,3,3,23,11,5,3,3,199,3,5,3,211,3,7,5,3,3 %N A023511 Least odd prime divisor of prime(n) + 1, or 1 if prime(n) + 1 is a power of 2. %C A023511 Note that a(n) = 1 for n= 2, 4, 11, 31, 1028, ... (A059305). - _Michel Marcus_, Oct 01 2013 %F A023511 a(n) = A078701(A008864(n)). - _Michel Marcus_, Jun 06 2019 %o A023511 (PARI) a(n) = my(p = prime(n) + 1, v = p/(2^valuation(p, 2))) ; if (v == 1, 1, factor(v)[1, 1]); \\ _Michel Marcus_, Oct 01 2013 %Y A023511 Cf. A008864, A078701. %K A023511 nonn %O A023511 1,1 %A A023511 _Clark Kimberling_