A171761 Number of ternary squareful words of length n.

0, 0, 3, 15, 63, 213, 687, 2127, 6483, 19575, 58905, 176943, 531177, 1593981, 4782513, 14348289, 43045923, 129139119, 387419097, 1162259637, 3486782013, 10460350023, 31381055463, 94143173409

Offset

0,3

Links

Table of n, a(n) for n=0..23.

Formula

a(n) = A000244(n) - A006156(n).

Mathematica

nmax = 23; 3^Range[0, nmax] - Length /@ NestList[ DeleteCases[ Flatten[ Outer[ Append, #, {1, 2, 3}, 1], 1], {___, x__, x__, ___}] &, {{}}, nmax] (* Jean-François Alcover, Jun 12 2017, using Vladimir Reshetnikov's code for A006156 *)

Crossrefs

Cf. A000244, A006156.

Sequence in context: A260326 A204086 A379242 * A229277 A218313 A218190

Adjacent sequences: A171758 A171759 A171760 * A171762 A171763 A171764

Keyword

nonn

Author

Mats Granvik, Dec 18 2009

Status

approved