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 A127396 #17 Feb 16 2025 08:33:04
%S A127396 0,0,1,2,7,13,30,60,125,256,513,1049,2082,4214,8401,16771,33427,66550,
%T A127396 132405,262865,522296,1036033,2055256,4075039,8078110,16008485,
%U A127396 31720903,62847087,124501149,246638355,488559079,967785236,1917099175,3797688543
%N A127396 Number of 3-almostprimes <= 2^n.
%H A127396 Robert G. Wilson v, <a href="/A127396/b127396.txt">Table of n, a(n) for n = 1..53</a>
%H A127396 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Semiprime.html">Semiprime</a>.
%F A127396 a(n) = A072114(2^n). - _R. J. Mathar_, Aug 26 2011
%t A127396 ThreeAlmostPrimePi[n_] := Sum[PrimePi[n/(Prime@i*Prime@j)] - j + 1, {i, PrimePi[n^(1/3)]}, {j, i, PrimePi[Sqrt[n/Prime@i]]}]; Table[ ThreeAlmostPrimePi[2^n], {n, 30}]
%Y A127396 Cf. A126279, A109251, A125527.
%K A127396 nonn,less
%O A127396 1,4
%A A127396 _Robert G. Wilson v_, Dec 29 2006