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%I #19 Sep 10 2017 05:55:10
%S 2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,24,25,26,27,
%T 28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,48,49,50,51,52,
%U 54,55,56,57,58,59,60,62,63,64,65,66,67,68,70,72,73,74,75,76,78,80,81,82
%N Numbers that can be written as sum of two 3-smooth numbers.
%C A081326(a(n)) > 0; complement of A081329.
%H Charles R Greathouse IV, <a href="/A081330/b081330.txt">Table of n, a(n) for n = 1..10000</a>
%H Ivars Peterson, <a href="http://www.sciencenews.org/sn_arc99/1_23_99/mathland.htm">Medieval Harmony</a>. [Broken link]
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/SmoothNumber.html">Smooth Number</a>.
%F a(n) >> exp(n^(1/4)). - _Charles R Greathouse IV_, Aug 22 2011
%t max = 100; Table[2^i *3^j + 2^k* 3^l, {i, 0, Log[2, max] // Ceiling}, {j, 0, Log[3, max] // Ceiling}, {k, 0, Log[2, max] // Ceiling}, {l, 0, Log[3, max] // Ceiling}] // Flatten // Union // Select[#, # <= max &] & (* _Jean-François Alcover_, Sep 10 2017 *)
%o (PARI) list(lim)=my(v=List(), u=v, N); for(n=0, log(lim\1+.5)\log(3), N=3^n; while(N<=lim, listput(v, N); N<<=1)); v=Set(v); for(i=1,#v,for(j=i,#v, N=v[i]+v[j]; if(N>lim, break); listput(u,N))); Set(u) \\ _Charles R Greathouse IV_, Sep 07 2014
%Y Cf. A003586, A081332, A081333, A081327, A081328.
%K nonn
%O 1,1
%A _Reinhard Zumkeller_, Mar 19 2003
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