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 A377028 #10 Oct 16 2024 21:35:57
%S A377028 1,2,2,3,3,4,4,5,5,5,5,6,6,6,6,7,7,8,8,8,8,8,8,9,9,9,9,9,9,10,10,11,
%T A377028 11,11,11,12,12,12,12,12,12,12,12,12,12,12,12,13,13,13,13,13,13,14,14,
%U A377028 14,14,14,14,15,15,15,15,16,16,16,16,16,16,16,16,17,17
%N A377028 a(n) = number of integers k <= n such that k is a term in A055932.
%C A377028 Sequence counts the number of k <= n such that the squarefree kernel of k = rad(k) = A007947(k) is a primorial number (a term in A002110). Similar counting function to A000720 (number of primes <= n).
%H A377028 Michael De Vlieger, <a href="/A377028/b377028.txt">Table of n, a(n) for n = 1..10000</a>
%e A377028 a(30) = 10 because there are 10 numbers k <= 30 which are terms in A005932 (namely : 1,2,4,6,8,12,16,18,24,30).
%t A377028 c = 0; fQ[x_] := Or[IntegerQ@ Log2[x], And[EvenQ[x], Union@ Differences@ PrimePi[FactorInteger[x][[All, 1]] ] == {1}] ]; Reap[Do[If[fQ[n], c++]; Sow[c], {n, 10^4}] ][[-1, 1]] (* _Michael De Vlieger_, Oct 13 2024 *)
%Y A377028 Cf. A000720, A002110, A007947, A055932, A376690.
%K A377028 nonn
%O A377028 1,2
%A A377028 _David James Sycamore_, Oct 13 2024
%E A377028 More terms from _Michael De Vlieger_, Oct 13 2024