A261875 Decimal expansion of the coefficient 'gamma' (see formula) appearing in Otter's result concerning the asymptotics of T_n, the number of non-isomorphic rooted trees of order n.

2, 6, 8, 1, 1, 2, 8, 1, 4, 7, 2, 6, 7, 1, 1, 2, 2, 3, 8, 5, 7, 7, 3, 2, 8, 7, 8, 3, 7, 0, 3, 9, 3, 7, 0, 9, 3, 5, 4, 1, 7, 5, 3, 4, 7, 2, 0, 1, 1, 6, 1, 6, 6, 3, 5, 2, 7, 4, 9, 7, 0, 2, 5, 8, 8, 6, 4, 0, 2, 8, 4, 0, 3, 6, 5, 1, 6, 5, 3, 4, 5, 0, 6, 7, 2, 3, 9, 2, 0, 8, 5, 5, 8, 7, 7, 5, 9, 9, 1, 1

Offset: 1

Author

Jean-François Alcover, Sep 04 2015

Keywords

• cons
• nonn

Examples

			2.68112814726711223857732878370393709354175347201161663527497...
		

References

• Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 5.6 Otter's tree enumeration constants, p. 296.

Crossrefs

Cf. A000055, A000081, A051491, A086308, A187770.

Programs

Mathematica

digits = 100; max = 250; Clear[s, a]; s[n_, k_] := s[n, k] = a[n + 1 - k] + If[n < 2*k, 0, s[n-k, k]]; a[1] = 1; a[n_] := a[n] = Sum[a[k]*s[n-1, k]*k, {k, 1, n-1}]/(n-1); A[x_] := Sum[a[k]*x^k, {k, 0, max}]; APrime[x_] := Sum[k*a[k]*x^(k-1), {k, 0, max}]; eq = Log[c] == 1 + Sum[A[c^-k]/k, {k, 2, max}]; alpha = c /. FindRoot[eq, {c, 3}, WorkingPrecision -> digits+5]; beta = (1+Sum[APrime[alpha^(-k)]/alpha^k, {k, 2, max}])^(3/2)/Sqrt[2*Pi]; gamma = 2^(2/3)*Pi^(1/6)*beta^(1/3) * Sqrt[alpha]; RealDigits[gamma, 10, digits] // First

Formula

Lim_{n->infinity} T_n*n^(3/2)/alpha^n = (beta/(2 Pi))^(1/3) = (1/(4 Pi alpha))^(1/2)*gamma, where alpha is A051491 and beta is A086308.

gamma = 2^(2/3)*Pi^(1/6)*beta^(1/3)*sqrt(alpha).