A081328 Greatest 3-smooth number m such that n-m is also 3-smooth, a(n)=0 if no such 3-smooth number exists.

0, 1, 2, 3, 4, 4, 6, 6, 8, 9, 9, 9, 12, 12, 12, 12, 16, 16, 18, 18, 18, 18, 0, 18, 24, 24, 24, 27, 27, 27, 27, 24, 32, 32, 32, 32, 36, 36, 36, 36, 32, 36, 27, 36, 36, 0, 0, 36, 48, 48, 48, 48, 0, 48, 54, 54, 54, 54, 32, 54, 0, 54, 54, 48, 64, 64, 64, 64, 0, 64, 0, 64, 72, 72, 72, 72, 0

Offset

1,3

Links

Table of n, a(n) for n=1..77.

Formula

a(n)=0 iff A081326(n)=0; if a(n)>0: a(n)+A081327(n)=n.

Example

a(32) = 24 = 3*2^3, as 32 = 2^3 + 24.

Mathematica

smooth3Q[n_] := n == 2^IntegerExponent[n, 2]*3^IntegerExponent[n, 3];
a[n_] := Module[{m}, For[m = n, m >= 1, m--, If[smooth3Q[m], If[smooth3Q[n - m], Return[m]]]]; 0];
Array[a, 77] (* Jean-François Alcover, Oct 17 2021 *)

Crossrefs

Cf. A081329, A081330, A081327, A000040, A003586.

Sequence in context: A102441 A102440 A124815 * A179276 A213635 A218443

Adjacent sequences: A081325 A081326 A081327 * A081329 A081330 A081331

Keyword

nonn

Author

Reinhard Zumkeller, Mar 19 2003

Status

approved