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 A109399 #30 Jul 22 2024 15:24:27
%S A109399 216,1000,1080,1512,2376,2744,2808,3000,3375,3672,4104,4968,5400,6264,
%T A109399 6696,6750,7000,7560,7992,8232,8856,9000,9261,9288,10152,10584,10648,
%U A109399 11000,11448,11880,12744,13000,13176,13500,13720,14040,14472,15336,15768,16632,17000,17064,17576,17928,18360,18522,19000,19224,19656,20520,20952,21000,21816,22248,23000,23112,23544,23625,24408,24696,24840,25704,26136,27000
%N A109399 Numbers with at least two 3s in their prime signature.
%C A109399 In other words, if the canonical prime factorization of a term into prime powers is Product p(i)^e(i), then e(i) = 3 for at least two values of i.
%C A109399 Does not include all numbers with at least two unitary prime power divisors that are cubes (see example section).
%C A109399 The asymptotic density of this sequence is 1 - (1 + Sum_{p prime} ((p-1)/(p^4-p+1))) * Product_{p prime} (1-1/p^3+1/p^4) = 0.0024593812036570543518... . - _Amiram Eldar_, Jul 22 2024
%H A109399 Vincenzo Librandi, <a href="/A109399/b109399.txt">Table of n, a(n) for n = 1..1000</a>
%e A109399 216 = 2^3*3^3, 1000 = 2^3*5^3, 1080 = 2^3*3^3*5, ...
%e A109399 On the other hand, 1728 = 2^6*3^3, 8000 = 2^6*5^3 and 21952 = 2^6*7^3 are not in the sequence.
%t A109399 f[n_]:=Count[Last/@FactorInteger[n],3]>1; Select[Range[8!],f]
%o A109399 (PARI) is(n)=#select(e->e==3, factor(n)[,2])>1 \\ _Charles R Greathouse IV_, Oct 19 2015
%Y A109399 Cf. A000578, A001235, A176297, A176313, A176350.
%Y A109399 A176359 is a subsequence.
%K A109399 nonn,easy
%O A109399 1,1
%A A109399 _Vladimir Joseph Stephan Orlovsky_, Dec 07 2010
%E A109399 Edited by _Matthew Vandermast_, Dec 07 2010