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 A382769 #4 Apr 05 2025 10:58:53
%S A382769 0,0,0,0,0,0,0,0,0,6,0,10,0,12,12,0,0,15,0,18,18,20,0,22,0,24,0,26,0,
%T A382769 28,0,0,30,30,30,34,0,36,36,38,0,40,0,42,42,44,0,46,0,48,48,50,0,52,
%U A382769 50,54,54,56,0,58,0,60,60,0,60,63,0,66,66,68,0,70,0,72
%N A382769 Largest k < n such that gcd(k,n) > 1 and rad(k) does not divide n, where rad = A007947, or 0 if k does not exist.
%H A382769 Michael De Vlieger, <a href="/A382769/b382769.txt">Table of n, a(n) for n = 1..10000</a>
%F A382769 a(n) = 0 for n = 6, and n in A000961.
%F A382769 For n > 6 in A024619, a(n) is the last term in row n of A272619.
%t A382769 rad[x_] := rad[x] = Times @@ FactorInteger[x][[All, 1]]; {0}~Join~Table[If[Nor[PrimePowerQ[n], n == 6], k = n - 2; While[Or[CoprimeQ[n, k], Divisible[n, rad[k]]], k--]; k, 0], {n, 2, 120}]
%Y A382769 Cf. A000961, A024619, A096014, A272619.
%K A382769 nonn,easy
%O A382769 1,10
%A A382769 _Michael De Vlieger_, Apr 04 2025