A007168 P-graphs with 2n edges. (Formerly M1774)

1, 2, 7, 26, 114, 512, 2427, 11794, 58787, 298188, 1535962, 8009527, 42209709, 224435066, 1202611161, 6487520874, 35204691958, 192042016789, 1052495823168, 5792479501760, 32000066582116, 177388902951224, 986412534845206, 5500872578870102

Offset

1,2

References

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

Table of n, a(n) for n=1..24.

R. C. Read, On the enumeration of a class of plane multigraphs, Aequat. Math. 31 (1986) no 1, 47-63.

Prog

(PARI) { s =y ; for(loop=1, 18, p = 1 ; forstep(i= 1, 2*loop-1, 2, sigmai = polcoeff(s, i, y) ; n=0 ; tmp = 0 ; while(i*n <=2*loop-1, ff = 1 ; for(k=1, n, ff *= (-sigmai-k+1)/k ; ) ; tmp += ff*(-y)^(i*n) ; n++ ; ) ; p *= tmp : ) ; print1(polcoeff(p, 2*loop-2, y), ", ") ; b = y-s ; forstep(i=1, 2*loop-1, 2, b += polcoeff(p, i, y)*y^i ; ) ; s = y ; for(r=0, loop-1, for(i=0, 2*loop+1, s += polcoeff(b^(3+2*r), i, y)*y^i ; ) ; ) ; ) ; } \\ R. J. Mathar, Apr 24 2006

Crossrefs

Sequence in context: A001862 A150588 A150589 * A150590 A202830 A006373

Adjacent sequences: A007165 A007166 A007167 * A007169 A007170 A007171

Keyword

nonn

Author

N. J. A. Sloane

Extensions

More terms from R. J. Mathar, Apr 24 2006

More terms from Sean A. Irvine, Nov 07 2017

Status

approved