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 A036649 Number of bicentered 5-valent trees with n nodes. 2
 0, 0, 1, 0, 1, 1, 3, 4, 10, 18, 46, 95, 231, 524, 1287, 3095, 7713, 19125, 48258, 122026, 311935, 801061, 2072629, 5387753, 14081981, 36959506, 97419796, 257724555, 684254908, 1822560590, 4869517848, 13047469920, 35053803135 (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. FORMULA a(n) = A036650(n) - A036648(n). MATHEMATICA n = 30; (* algorithm from Rains and Sloane *) S4[f_, h_, x_] := f[h, x]^4/24 + f[h, x]^2 f[h, x^2]/4 + f[h, x] f[h, x^3]/3 + f[h, x^2]^2/8 + f[h, x^4]/4; T[-1, z_] := 1;  T[h_, z_] := T[h, z] = Table[z^k, {k, 0, n}].Take[CoefficientList[z^(n+1) + 1 + S4[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 Cf. A036648, A036650. Sequence in context: A171160 A139797 A306334 * A345322 A255539 A326832 Adjacent sequences:  A036646 A036647 A036648 * A036650 A036651 A036652 KEYWORD nonn AUTHOR STATUS approved

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Last modified August 9 18:55 EDT 2022. Contains 356026 sequences. (Running on oeis4.)