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 A363217 #17 May 28 2023 20:49:33
%S A363217 225,441,675,1089,1125,1225,1323,1521,2025,2601,3025,3087,3249,3267,
%T A363217 3375,3969,4225,4563,4761,5625,5929,6075,6125,7225,7569,7803,8281,
%U A363217 8575,8649,9025,9261,9747,9801,10125,11025,11907,11979,12321,13225,13689,14161,14283,15125,15129,16641,16875,17689,18225,19773
%N A363217 Odd powerful numbers that are not powers of primes.
%C A363217 This sequence is { A286708 INTERSECT A005408 } = { A001694 INTERSECT A360769 }.
%C A363217 Subset of A001694, A062739, A126706, and A360769.
%H A363217 Michael De Vlieger, <a href="/A363217/b363217.txt">Table of n, a(n) for n = 1..10000</a>
%F A363217 This sequence is { k = a^2*b^3 : a >= 1, b >= 1, omega(k) > 1, k mod 2 = 1 }.
%F A363217 Sum_{n>=1} 1/a(n) = 2*zeta(2)*zeta(3)/(3*zeta(6)) - 1/2 - Sum_{p prime} 1/(p*(p-1)) = (2/3) * A082695 - 1/2 - A136141 = 0.0225742... . - _Amiram Eldar_, May 28 2023
%e A363217 a(1) = 225 = 3^2 * 5^2, the smallest odd number with multiple distinct prime factors, each of which have multiplicity exceeding 1.
%e A363217 a(2) = 441 = 3^2 * 7^2,
%e A363217 a(3) = 675 = 3^3 * 5^2, etc.
%t A363217 With[{nn = 20000}, Select[Union@ Flatten@ Table[a^2*b^3, {b, nn^(1/3)}, {a, Sqrt[nn/b^3]}], And[OddQ[#], ! PrimePowerQ[#]] &] ]
%o A363217 (PARI) isok(k) = (k>1) && (k%2) && ispowerful(k) && !isprimepower(k); \\ _Michel Marcus_, May 28 2023
%Y A363217 Cf. A000961, A001694, A062739, A126706, A286708, A363216.
%Y A363217 Cf. A002117, A013661, A013664, A082695, A136141.
%K A363217 nonn
%O A363217 1,1
%A A363217 _Michael De Vlieger_, May 21 2023