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 A081504 #9 Mar 10 2015 12:36:48 %S A081504 8,25,32,40,43,48,56,58,64,96,104,112,120,128,134,140,145,152,160,176, %T A081504 185,192,208,212,224,235,240,244,248,252,256,264,272,280,286,288,292, %U A081504 302,304,308,320,326,332,348,356,360,384,392,394,400,416,418,432,448 %N A081504 Numbers n such that there are no primes of the form 2^n+2^i+1 for 0<i<n. In binary: all 3-bit numbers with size n+1 are composite. %C A081504 There seem to be no such numbers (bit sizes) such that any 4-bit or 5-bit number is composite, up to n around 200. %H A081504 T. D. Noe, <a href="/A081504/b081504.txt">Table of n, a(n) for n=1..265</a> %o A081504 (PARI) for(n=2, 1000, f=0; for(i=1, n-1, t=2^n+2^i+1; if(isprime(t), f=1; break)); if(!f, print1(n", "))) %Y A081504 Cf. A081091, A081092. %K A081504 nonn %O A081504 1,1 %A A081504 _Ralf Stephan_, Apr 21 2003