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A339297
Triangle read by rows: T(n,k) is the number of oriented series-parallel networks with n colored elements and without multiple unit elements in parallel using exactly k colors.
2
1, 1, 2, 2, 12, 12, 5, 64, 162, 108, 13, 354, 1734, 2760, 1380, 36, 1992, 16977, 48716, 56100, 22440, 103, 11538, 161691, 746316, 1488240, 1338120, 446040, 306, 68427, 1524969, 10652086, 32760180, 49718640, 36614760, 10461360, 930, 414294, 14382720, 146464740, 652517010, 1487453760, 1816345440, 1131883200, 282970800
OFFSET
1,3
COMMENTS
A series configuration is an ordered concatenation of two or more parallel configurations and a parallel configuration is a multiset of two or more unit elements or series configurations. In this variation, parallel configurations may include the unit element only once. T(n, k) is the number of series or parallel configurations with n unit elements of k colors using each color at least once.
EXAMPLE
Triangle begins:
1;
1, 2;
2, 12, 12;
5, 64, 162, 108;
13, 354, 1734, 2760, 1380;
36, 1992, 16977, 48716, 56100, 22440;
103, 11538, 161691, 746316, 1488240, 1338120, 446040;
...
PROG
(PARI) \\ R(n, k) gives colorings using at most k colors as a vector.
EulerT(v)={Vec(exp(x*Ser(dirmul(v, vector(#v, n, 1/n))))-1, -#v)}
R(n, k)={my(Z=k*x, p=Z+O(x^2)); for(n=2, n, p = Z + (1 + Z)*x*Ser(EulerT( Vec(p^2/(1+p), -n) ))); Vec(p)}
M(n)={my(v=vector(n, k, R(n, k)~)); Mat(vector(n, k, sum(i=1, k, (-1)^(k-i)*binomial(k, i)*v[i])))}
{my(T=M(8)); for(n=1, #T~, print(T[n, 1..n]))}
CROSSREFS
Column 1 is A339290.
Main diagonal is A339301.
Row sums are A339298.
Cf. A339228.
Sequence in context: A228154 A275279 A109767 * A196061 A342582 A131121
KEYWORD
nonn,tabl
AUTHOR
Andrew Howroyd, Dec 22 2020
STATUS
approved