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 A365677 #60 Oct 24 2023 12:57:09
%S A365677 0,0,0,1,1,1,1,3,5,5,5,6,6,6,6,11,11,13,13,14,14,14,14,16,20,20,24,25,
%T A365677 25,25,25,31,31,31,31,36,36,36,36,38,38,38,38,39,41,41,41,46,52,56,56,
%U A365677 57,57,61,61,63,63,63,63,64,64,64,66,79,79,79,79,80,80,80,80,86,86,86,90,91,91
%N A365677 Number of increasing geometric progressions in {1,2,3,...,n} with rational ratio and length >= 3.
%H A365677 Scott R. Shannon, <a href="/A365677/b365677.txt">Table of n, a(n) for n = 1..1000</a>
%F A365677 a(n) = A366471(n) - n*(1 + (n-1)/2) = Sum_{k=3 .. 1+floor(log_2(n))} Sum_{p=2..floor(n^(1/(k-1)))} phi(p)*floor(n/p^(k-1)), where phi is the Euler phi-function A000010.
%e A365677 a(9) = 5 as {1,2,...,9} contains the geometric progressions [1,2,4], [1,2,4,8], [2,4,8], [1,3,9], [4,6,9].
%Y A365677 Cf. A366471, A078651, A051336.
%K A365677 nonn
%O A365677 1,8
%A A365677 _Scott R. Shannon_ and _N. J. A. Sloane_, Oct 23 2023