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A007168 P-graphs with 2n edges.
(Formerly M1774)
0
1, 2, 7, 26, 114, 512, 2427, 11794, 58787, 298188, 1535962, 8009527, 42209709, 224435066, 1202611161, 6487520874, 35204691958 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

R. C. Read, On the enumeration of a class of plane multigraphs, Aequat. Math., 31 (1986), 47-63.

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..17.

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

STATUS

approved

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Last modified November 26 16:10 EST 2014. Contains 250079 sequences.