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 A120048 #12 Mar 18 2025 14:55:24
%S A120048 0,0,0,14,231,2973,35585,409849,4600247,50678212,550454756,5913771637,
%T A120048 62981797962,665997804082,7001087934965,73232029374751,
%U A120048 762783057783010,7916319351632036,81898808371556517
%N A120048 Number of 7-almost primes less than or equal to 10^n.
%e A120048 There are 14 seven-almost primes up to 1000: 128, 192, 288, 320, 432, 448, 480, 648, 672, 704, 720, 800, 832 & 972.
%t A120048 AlmostPrimePi[k_Integer, n_] := Module[{a, i}, a[0] = 1; If[k == 1, PrimePi[n], Sum[PrimePi[n/Times @@ Prime[Array[a, k - 1]]] - a[k - 1] + 1, Evaluate[ Sequence @@ Table[{a[i], a[i - 1], PrimePi[(n/Times @@ Prime[Array[a, i - 1]])^(1/(k - i + 1))]}, {i, k - 1}]]]]]; (* _Eric W. Weisstein_, Feb 07 2006 *)
%t A120048 Table[AlmostPrimePi[7, 10^n], {n, 11}]
%Y A120048 Cf. A066265, A014613, A116382.
%Y A120048 Cf. A006880, A036352, A109251, A114106, A114453, A120047, A120048, A120049, A120050, A120051, A120052, A120053, A116430.
%K A120048 nonn
%O A120048 0,4
%A A120048 _Robert G. Wilson v_, Feb 07 2006
%E A120048 More terms from _Robert G. Wilson v_, Jan 07 2007
%E A120048 Example corrected by _Harvey P. Dale_, Jan 25 2013
%E A120048 a(15)-a(18) from _Henri Lifchitz_, Mar 18 2025