OFFSET
1,12
COMMENTS
Permuting the colors does not change the structure.
The definition requires that a necklace must not be equivalent to itself by permutation of colors and rotation (except for identity rotation). For example the length 2 necklace AB is excluded because a rotation of 1 gives BA and permutation of colors brings back to AB.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..1275
EXAMPLE
Triangle begins:
1;
0, 0;
0, 1, 0;
0, 1, 1, 0;
0, 3, 5, 2, 0;
0, 4, 13, 9, 2, 0;
0, 9, 43, 50, 20, 3, 0;
0, 14, 116, 206, 127, 31, 3, 0;
0, 28, 335, 862, 772, 293, 51, 4, 0;
0, 48, 920, 3384, 4226, 2263, 580, 72, 4, 0;
...
T(6, 4) = 9: {aaabcd, aabacd, aabcad, aabbcd, aabcbd, aabcdb, aacbdb, ababcd, abacbd}. Compared with A107424 the patterns {abacad, aacbbd, abcabd, acabdb} are excluded.
PROG
(PARI)
R(n) = {Mat(Col([Vecrev(p/y, n) | p<-Vec(intformal(sum(m=1, n, moebius(m) * subst(serlaplace(-1 + exp(sumdiv(m, d, y^d*(exp(d*x + O(x*x^(n\m)))-1)/d))), x, x^m))/x))]))}
{ my(A=R(12)); for(n=1, #A, print(A[n, 1..n])) }
KEYWORD
nonn,tabl
AUTHOR
Andrew Howroyd, Sep 22 2019
STATUS
approved