OFFSET
1,4
COMMENTS
A multiset is periodic if its multiplicities have a common divisor greater than 1.
EXAMPLE
The a(6) = 9 periodic multisets of compositions are:
{1,1,1,1,1,1},
{1,1,2,2}, {1,1,11,11},
{2,2,2}, {11,11,11},
{3,3}, {21,21}, {12,12}, {111,111}.
MATHEMATICA
nn=60;
ser=Product[1/(1-x^n)^2^(n-1), {n, nn}]
Table[SeriesCoefficient[ser, {x, 0, n}]-Sum[MoebiusMu[d]*SeriesCoefficient[ser, {x, 0, n/d}], {d, Divisors[n]}], {n, 1, nn}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Apr 26 2018
STATUS
approved