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 A377730 #8 Feb 16 2025 08:34:07
%S A377730 0,0,0,1,0,1,0,2,2,1,0,3,0,1,2,3,0,4,0,3,2,1,0,5,4,1,6,3,0,5,0,4,2,1,
%T A377730 4,7,0,1,2,6,0,5,0,3,7,1,0,8,6,8,2,3,0,9,4,7,2,1,0,9,0,1,8,5,4,5,0,3,
%U A377730 2,9,0,10,0,1,10,3,6,5,0,11,11,1,0,10,4,1,2,7,0,12
%N A377730 Number of integers less than n that have the same greatest prime factor as n.
%H A377730 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/GreatestPrimeFactor.html">Greatest Prime Factor</a>
%F A377730 a(n) = |{j < n : gpf(j) = gpf(n)}|.
%F A377730 a(n) = A078899(n) - 1.
%p A377730 R:= NULL:
%p A377730 for n from 1 to 100 do p:= max(numtheory:-factorset(n)); if assigned(C[p]) then C[p]:= C[p]+1 else C[p]:= 0 fi;
%p A377730 R:= R, C[p]
%p A377730 od:R; # _Robert Israel_, Nov 07 2024
%t A377730 Table[Length[Select[Range[n - 1], FactorInteger[#][[-1, 1]] == FactorInteger[n][[-1, 1]] &]], {n, 90}]
%Y A377730 Cf. A006530, A047983, A078899, A334655, A335097, A377734.
%K A377730 nonn
%O A377730 1,8
%A A377730 _Ilya Gutkovskiy_, Nov 05 2024