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%I #25 Oct 19 2015 17:20:01
%S 216,1000,1080,1512,2376,2744,2808,3000,3375,3672,4104,4968,5400,6264,
%T 6696,6750,7000,7560,7992,8232,8856,9000,9261,9288,10152,10584,10648,
%U 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 Numbers with at least two 3s in their prime signature.
%C In other words, if the canonical prime factorization of n into prime powers is Product p(i)^e(i), then e(i) = 3 for at least two values of i.
%C Does not include all numbers with at least two unitary prime power divisors that are cubes (see example section).
%H Vincenzo Librandi, <a href="/A109399/b109399.txt">Table of n, a(n) for n = 1..1000</a>
%e 216=2^3*3^3, 1000=2^3*5^3, 1080=2^3*3^3*5,...
%e 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 f[n_]:=Count[Last/@FactorInteger[n],3]>1; Select[Range[8!],f]
%o (PARI) is(n)=#select(e->e==3, factor(n)[,2])>1 \\ _Charles R Greathouse IV_, Oct 19 2015
%Y Cf. A000578, A001235, A176297, A176313, A176350.
%K nonn,easy
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Dec 07 2010
%E Edited by _Matthew Vandermast_, Dec 07 2010
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