OFFSET
0,3
LINKS
E. de Panafieu and S. Dovgal, Symbolic method and directed graph enumeration, arXiv:1903.09454 [math.CO], 2019.
R. W. Robinson, Counting digraphs with restrictions on the strong components, Combinatorics and Graph Theory '95 (T.-H. Ku, ed.), World Scientific, Singapore (1995), 343-354.
Wikipedia, Strongly connected component
FORMULA
EXAMPLE
1;
0, 2;
0, 4, 12;
0, 144, 168, 200;
0, 25696, 18768, 12384, 8688;
...
MATHEMATICA
nn =15; strong = Select[Import["https://oeis.org/A003030/b003030.txt", "Table"],
Length@# == 2 &][[All, 2]]; s[x_] := Total[strong Table[x^i/i!, {i, 1, 58}]]; begf = Total[CoefficientList[ Series[1/(Total[CoefficientList[Series[ Exp[-u *s[x]], {x, 0, nn}], x]* Table[z^n/(2^Binomial[n, 2]), {n, 0, nn}]]), {z, 0, nn}], z]*Table[z^n 2^Binomial[n, 2], {n, 0, nn}]] /. z -> 2 z;
Range[0, nn]! CoefficientList[begf, {z, u}] // Grid (* Geoffrey Critzer, Mar 14 2023 after Andrew Howroyd *)
PROG
(PARI)
Z(p, f)={my(n=serprec(p, x)); serconvol(p, sum(k=0, n-1, x^k*f(k), O(x^n)))}
G(e, p)={Z(p, k->1/e^(k*(k-1)/2))}
U(e, p)={Z(p, k->e^(k*(k-1)/2))}
RelEgf(n, e)={sum(k=0, n, e^(k^2)*x^k/k!, O(x*x^n) )}
T(n)={my(e=2); [Vecrev(p) | p<-Vec(serlaplace(U(e, 1/G(e, exp(y*log(U(e, 1/G(e, RelEgf(n, e)))))))))]}
{ my(A=T(6)); for(i=1, #A, print(A[i])) } \\ Andrew Howroyd, Mar 06 2023
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Geoffrey Critzer, Mar 06 2023
EXTENSIONS
Terms a(15) and beyond from Andrew Howroyd, Mar 06 2023
STATUS
approved