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 A210684 #25 May 15 2012 11:06:23
%S A210684 0,7,101,864,7365,63331,554839,4931118,44339730,402709395,3687732409,
%T A210684 34007530868
%N A210684 Number of primes p < 10^n such that both 2*p+1 and 4*p+1 are composite.
%F A210684 a(n) = A006880(n) - A092816(n) - A182265(n) + 1.
%F A210684 a(n) ~ 10^n / (n log 10). - _Charles R Greathouse IV_, May 11 2012
%t A210684 f[n_] := Length[Select[Range[10^n], PrimeQ[#] && !PrimeQ[2#+1] && !PrimeQ[4#+1]&]]; Table[f[n], {n,7}]
%Y A210684 Cf. A006880, A092816, A182265, A156660, A005384, A156874.
%K A210684 nonn
%O A210684 1,2
%A A210684 _Enrique Pérez Herrero_, May 09 2012