A081330 Numbers that can be written as sum of two 3-smooth numbers.

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, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 59, 60, 62, 63, 64, 65, 66, 67, 68, 70, 72, 73, 74, 75, 76, 78, 80, 81, 82

Offset

1,1

Comments

A081326(a(n)) > 0; complement of A081329.

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Ivars Peterson, Medieval Harmony. [Broken link]

Eric Weisstein's World of Mathematics, Smooth Number.

Formula

a(n) >> exp(n^(1/4)). - Charles R Greathouse IV, Aug 22 2011

Mathematica

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 *)

Prog

(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

Crossrefs

Cf. A003586, A081332, A081333, A081327, A081328.

Sequence in context: A132264 A214922 A004830 * A359415 A080682 A182049

Adjacent sequences: A081327 A081328 A081329 * A081331 A081332 A081333

Keyword

nonn

Author

Reinhard Zumkeller, Mar 19 2003

Status

approved