A000671 - OEIS

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A000671

Number of boron trees with n nodes, i.e. n-node rooted trees with degree <= 3 at root and out-degree <= 2 elsewhere.
(Formerly M1083 N0411)

0, 1, 1, 2, 4, 7, 14, 29, 60, 127, 275, 598, 1320, 2936, 6584, 14858, 33744, 76999, 176557, 406456, 939241, 2177573, 5064150, 11809632, 27610937, 64705623, 151966597, 357623905, 843176524, 1991439229, 4711115672, 11162025770, 26484061667, 62923251955

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OFFSET

0,4

COMMENTS

The subsequence of primes begins: 2, 7, 29, 127, 176557, 2177573, 151966597.

REFERENCES

A. Cayley, On the analytical forms called trees, with application to the theory of chemical combinations, Reports British Assoc. Advance. Sci. 45 (1875), 257-305 = Math. Papers, Vol. 9, 427-460 (see p. 450).

R. C. Read, personal communication.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

T. D. Noe, Table of n, a(n) for n = 0..200

S. J. Cyvin, J. Brunvoll, and B. N. Cyvin, Enumeration of constitutional isomers of polyenes, J. Molec. Struct. (Theochem) 357, no. 3 (1995) 255-261.

R. C. Read, Letter to N. J. A. Sloane, Oct. 29, 1976

Index entries for sequences related to trees

Index entries for sequences related to rooted trees

FORMULA

G.f.: A(x) = x*(1/3!)*(f^3+3*subs(x=x^2, f)*f+2*subs(x=x^3, f)), where f = G001190(x)/x, G001190 = g.f. for A001190.

a(n) = A001190(n) + A036657(n) + A036658(n).

Another g.f.: let B0(x) = 1+x, G036656(x) = g.f. for A036656, G036657(x) = g.f. for A036657.

Then g.f.: x*(cycle_index(S3, B0)+cycle_index(S3, G036656)+cycle_index(S3, G036657)+cycle_index(S2, B0)*(G036656+G036657)+cycle_index(S2, G036656)*(G036657+B0)+cycle_index(S2, G036657)*(B0+G036656)+B0*G036656*G036657), where cycle_index(Sk, f) means apply the cycle index for the symmetric group S_k to f(x).

E.g., cycle_index(S2, f) = (1/2!)*(f^2+subs(x=x^2, f), cycle_index(S3, f) = (1/3!)*(f^3+3*subs(x=x^2, f)*f+2*subs(x=x^3, f)).

MAPLE

N := 40: t1 := G001190/x: G000671 := series(x*(1/3!)*(t1^3+3*subs(x=x^2, t1)*t1+2*subs(x=x^3, t1)), x, N); A000671 := n->coeff(G000671, x, n);

CI2 := proc(f) (1/2)*(f^2+subs(x=x^2, f)); end; CI3 := proc(f) (1/6)*(f^3+3*subs(x=x^2, f)*f+2*subs(x=x^3, f)); end;

N := 40: B0 := series(1 + x, x, N): G000671 := series(x*(CI3(B0) + CI3(G036656) + CI3(G036657) + CI2(B0)*(G036656 + G036657) + CI2(G036656)*(G036657 + B0) + CI2(G036657)*(B0 + G036656) + B0*G036656*G036657), x, N); A036658 := n->coeff(G036658, x, n);

MATHEMATICA

terms = 32; (* B = g.f. for A001190 *) B[_] = 0; Do[B[x_] = x + (1/2)*(B[x]^2 + B[x^2]) + O[x]^terms // Normal, terms];

f[x_] = B[x]/x;

A[x_] = x*(1/3!)*(f[x]^3 + 3*f[x^2]*f[x] + 2*f[x^3]) + O[x]^terms;

CoefficientList[A[x], x] (* Jean-François Alcover, May 29 2012, from first g.f., updated Jan 10 2018 *)

CROSSREFS

Cf. A001190, A036657, A036658.

Sequence in context: A002989 A293336 A321401 * A199888 A157133 A367462

Adjacent sequences: A000668 A000669 A000670 * A000672 A000673 A000674

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane

STATUS

approved