A081327 Smallest 3-smooth number m such that n-m is also 3-smooth, a(n)=0 if no such 3-smooth number exists.

0, 1, 1, 1, 1, 2, 1, 2, 1, 1, 2, 3, 1, 2, 3, 4, 1, 2, 1, 2, 3, 4, 0, 6, 1, 2, 3, 1, 2, 3, 4, 8, 1, 2, 3, 4, 1, 2, 3, 4, 9, 6, 16, 8, 9, 0, 0, 12, 1, 2, 3, 4, 0, 6, 1, 2, 3, 4, 27, 6, 0, 8, 9, 16, 1, 2, 3, 4, 0, 6, 0, 8, 1, 2, 3, 4, 0, 6, 0, 8, 9, 1, 2, 3, 4, 32, 6, 16, 8, 9, 27, 0, 12, 0, 0, 24, 1, 2, 3, 4, 0

Offset: 1

Author

Reinhard Zumkeller, Mar 19 2003

Keywords

• nonn

Examples

			a(32) = 8 = 2^3, as 32 = 8 + 3*2^3.
		

Crossrefs

Cf. A081329, A081330, A081328, A000040, A003586.

Programs

Mathematica

smooth3Q[n_] := n/2^IntegerExponent[n, 2]/3^IntegerExponent[n, 3] == 1;
a[n_] := Module[{m}, For[m = 1, mJean-François Alcover, Oct 14 2021 *)

Formula

a(n) = 0 iff A081326(n) = 0.

If a(n) > 0: a(n)+A081328(n) = n.