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 A128997 #3 Mar 31 2012 13:48:30 %S A128997 11,12,15,20,21,22,23,24,25,28,29,30,33,35,36,37,39,40,41,42,43,44,45, %T A128997 46,47,48,50,51,52,53,55,56,57,58,59,60,63,64,65,66,67,68,69,70,71,72, %U A128997 73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,90,91,92,93,94,95,96 %N A128997 indices k such that A063670(k) differs from A005420(k). %C A128997 Primes in this sequence are those for which A005420(n) < 2^n-1, i.e. 2^n-1 is not prime. %o A128997 (PARI) t=1;vector(100,i,until( A063670(t++) != A005420(t),);t) %Y A128997 Cf. A005420, A063670. %K A128997 nonn %O A128997 1,1 %A A128997 _M. F. Hasler_, Apr 30 2007