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 A156877 #9 Nov 06 2022 07:48:17
%S A156877 0,0,0,0,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,3,3,3,3,
%T A156877 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
%U A156877 3,3,3,3,3,3,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4
%N A156877 Number of primes <= n that are safe primes and also Sophie Germain primes.
%H A156877 Reinhard Zumkeller, <a href="/A156877/b156877.txt">Table of n, a(n) for n = 1..10000</a>
%F A156877 a(n) = A156874(n) + A156875(n) - A156876(n).
%F A156877 a(n) = Sum_{k=1..n} A156659(k)*A156660(k).
%e A156877 a(120) = #{5, 11, 23, 83} = 4.
%Y A156877 Cf. A059455, A005384, A005385, A000720.
%Y A156877 Cf. A156874, A156875, A156876, A156659, A156660.
%K A156877 nonn
%O A156877 1,11
%A A156877 _Reinhard Zumkeller_, Feb 18 2009