0,6

R. G. Busacker and T. L. Saaty, Finite Graphs and Networks,mcGraw-Hill, NY, 1965, p. 201 (they reproduce Cayley's mistakes).

A. Cayley, "On the mathematical theory of isomers", Phil. Mag. vol. 67 (1874), 444-447.

A. Cayley, "Ueber die analytischen Figuren, welche in der Mathematik Baeume genannt werden...", Chem. Ber. 8 (1875), 1056-1059.

H. R. Henze and C. M. Blair, The number of structurally isomeric alcohols of the methanol series, J. Amer. Chem. Soc., 53 (1931), 3042-3046.

H. R. Henze and C. M. Blair, The number of isomeric hydrocarbons of the methane series, J. Amer Chem Soc. 53 (1931) 3077-3085.

N. J. A. Sloane, Table of n, a(n) for n = 0..60

H. Bottomley, Illustration of initial terms of A000022, A000200, A000602

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.

N. J. A. Sloane, My favorite integer sequences, in Sequences and their Applications (Proceedings of SETA '98).

N. J. A. Sloane, Maple program and first 60 terms for A000022, A000200, A000598, A000602, A000678

Index entries for sequences related to trees

# We continue from the Maple code in A000678: Unordered 4-tuples of ternary trees with one of height i and others of height at most i-1:

N := 45: i := 1: while i<(N+1) do Tb := t[ i ]-t[ i-1 ]: Ts := t[ i ]-1: Q2 := series(Tb*Ts+O(z^(N+1)), z, 200): q2[ i ] := Q2: i := i+1; od: q2[ 0 ] := 0: q[ -1 ] := 0:

for i from 0 to N do c[ i ] := series(q[ i ]-q[ i-1 ]-q2[ i ]+O(z^(N+1)), z, 200); od:

# erase height information: i := 'i': cent := series(sum(c[ i ], i=0..N), z, 200); G000022 := cent; A000022 := n->coeff(G000022, z, n);

# continued in A000200.

A000022+A000200=A000602. Cf. A010372.

Adjacent sequences: A000019 A000020 A000021 this_sequence A000023 A000024 A000025

Sequence in context: A094485 A021819 A000021 this_sequence A034805 A051765 A077063

nonn,easy,nice

njas, E. M. Rains (rains(AT)caltech.edu)