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 A081218 #11 Mar 26 2025 08:28:19
%S A081218 1,3,7,7,15,23,26,31,47,62,79,119,123,127,167,241,255,287,341,359,511,
%T A081218 527,623,727,839,959,1023,1330,1367,1679,1847,2047,2186,2195,2207,
%U A081218 2399,2807,3122,3478,3719,4094,4487,4911,5039,5327,6239,6559,6857,6887,7919
%N A081218 Greatest squarefree number not exceeding n-th prime power which is not prime.
%H A081218 Amiram Eldar, <a href="/A081218/b081218.txt">Table of n, a(n) for n = 1..10000</a>
%F A081218 a(n) = A070321(A025475(n)).
%t A081218 f[n_] := Module[{k = n-1}, While[!SquareFreeQ[k], k--]; k]; Join[{1}, f /@ Select[Range[8000], CompositeQ[#] && PrimePowerQ[#] &]] (* _Amiram Eldar_, Mar 26 2025 *)
%Y A081218 Cf. A025475, A070321, A081217.
%K A081218 nonn
%O A081218 1,2
%A A081218 _Reinhard Zumkeller_, Mar 10 2003