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 A138301 #3 Mar 31 2012 13:22:05 %S A138301 1,2,4,11,37,145,673,3748,22875 %N A138301 Number of integers k < 10^n such that k*(k+1)-1 and k*(k+3)-1 are both first of twin primes. %e A138301 3*4-1=11 11 and 13 twin primes, 3*6-1=17 17 and 19 twin primes a(1)=1 %e A138301 15*16-1=239 239 and 241 twin primes, 15*18-1=269 269 and 271 twin primes a(2)=2 %Y A138301 Cf. A138303. %K A138301 nonn %O A138301 1,2 %A A138301 _Pierre CAMI_, Mar 14 2008