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 A036652 Number of bicentered 6-valent trees with n nodes. 3
 0, 0, 1, 0, 1, 1, 3, 4, 11, 19, 49, 103, 254, 583, 1445, 3506, 8815, 22082, 56286, 143822, 371354, 963250, 2516822, 6607348, 17440933, 46233833, 123090070, 328923702, 882114742, 2373351473, 6405275496, 17336081498, 47047112028 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,7 LINKS E. M. Rains and N. J. A. Sloane, On Cayley's Enumeration of Alkanes (or 4-Valent Trees)., J. Integer Sequences, Vol. 2 (1999), Article 99.1.1. E. M. Rains and N. J. A. Sloane, On Cayley's Enumeration of Alkanes (or 4-Valent Trees), J. Integer Sequences, Vol. 2 (1999), Article 99.1.1. MATHEMATICA n = 20; (* algorithm from Rains and Sloane *) S5[f_, h_, x_] := f[h, x]^5/120 + f[h, x]^3 f[h, x^2]/12 + f[h, x]^2 f[h, x^3]/6 + f[h, x] f[h, x^2]^2/8 + f[h, x] f[h, x^4]/4 + f[h, x^2] f[h, x^3]/6 + f[h, x^5]/5; T[-1, z_] := 1;  T[h_, z_] := T[h, z] = Table[z^k, {k, 0, n}].Take[CoefficientList[z^(n+1) + 1 + S5[T, h-1, z]z, z], n+1]; Sum[Take[CoefficientList[z^(n+1) + (T[h, z] - T[h-1, z])^2/2 + (T[h, z^2] - T[h-1, z^2])/2, z], n+1], {h, 0, n/2}] (* Robert A. Russell, Sep 15 2018 *) CROSSREFS A036652 = A036653 - A036651. Sequence in context: A060285 A025079 A222770 * A295962 A097072 A049977 Adjacent sequences:  A036649 A036650 A036651 * A036653 A036654 A036655 KEYWORD nonn AUTHOR STATUS approved

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Last modified June 16 19:43 EDT 2019. Contains 324155 sequences. (Running on oeis4.)