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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, 192042016789, 1052495823168, 5792479501760, 32000066582116, 177388902951224, 986412534845206, 5500872578870102 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS 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 EXTENSIONS More terms from R. J. Mathar, Apr 24 2006 More terms from Sean A. Irvine, Nov 07 2017 STATUS approved

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Last modified January 20 11:11 EST 2020. Contains 331083 sequences. (Running on oeis4.)