A036649 -id:A036649 - cp's OEIS frontend

A036650 Number of 5-valent trees with n nodes.

1, 1, 1, 1, 2, 3, 6, 10, 21, 42, 94, 204, 473, 1098, 2633, 6353, 15641, 38789, 97416, 246410, 628726, 1614292, 4171955, 10839366, 28308678, 74266477, 195667533, 517504253, 1373640355, 3658205088, 9772510063, 26181295237, 70330621171

Offset: 0

N. J. A. Sloane

nonn

Andrew Howroyd, Table of n, a(n) for n = 0..500
R. Otter, The number of trees, Ann. of Math. (2) 49 (1948), 583-599 discusses asymptotics.
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.
Index entries for sequences related to trees

Column k=5 of A144528; A036718 (rooted trees).

Cf. A036648, A036649.

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;
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 + S4[T,h-1,z]z, z], n+1];
Sum[Take[CoefficientList[z^(n+1) + S5[T,h-1,z]z - S5[T,h-2,z]z - (T[h-1,z] - T[h-2,z]) (T[h-1,z]-1),z], n+1], {h,1,n/2}] + PadRight[{0,1}, 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 *)
b[n_, i_, t_, k_] := b[n,i,t,k] = If[i<1, 0, Sum[Binomial[b[i-1,i-1,
  k,k] + j-1, j]* b[n-i*j, i-1, t-j, k], {j, 0, Min[t, n/i]}]];
b[0, i_, t_, k_] = 1; m = 4; (* m = maximum children *) n = 40;
gf[x_] = 1 + Sum[b[j-1,j-1,m,m]x^j,{j,1,n}]; (* G.f. for A036718 *)
ci[x_] = SymmetricGroupIndex[m+1, x] /. x[i_] -> gf[x^i];
CoefficientList[Normal[Series[gf[x] - (gf[x]^2 - gf[x^2])/2 + x ci[x],
{x, 0, n}]],x] (* Robert A. Russell, Jan 19 2023 *)

a(n) = A036648(n) + A036649(n) for n > 0.

G.f.: B(x) - cycle_index(S2,-B(x)) + x * cycle_index(S5,B(x)) = B(x) - (B(x)^2 - B(x^2)) / 2 + x * (B(x)^5 + 10*B(x)^3*B(x^2) + 15*B(x)*B(x^2)^2 + 20*B(x)^2*B(x^3) + 20*B(x^2)*B(x^3) + 30*B(x)*B(x^4) + 24*B(x^5)) / 120, where B(x) = 1 + x * cycle_index(S4,B(x)) = 1 + x * (B(x)^4 + 6*B(x)^2*B(x^2) + 8*B(x)*B(x^3) + 3*B(x^2)^2 + 6*B(x^4)) / 24 is the generating function for A036718. - Robert A. Russell, Jan 19 2023

a(0) changed to 1 by Andrew Howroyd, Dec 18 2020

A036648 Number of centered 5-valent trees with n nodes.

Original entry on oeis.org

0, 1, 0, 1, 1, 2, 3, 6, 11, 24, 48, 109, 242, 574, 1346, 3258, 7928, 19664, 49158, 124384, 316791, 813231, 2099326, 5451613, 14226697, 37306971, 98247737, 259779698, 689385447, 1835644498, 4902992215, 13133825317, 35276818036

Offset: 0

N. J. A. Sloane

nonn

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.
Index entries for sequences related to trees

Cf. A036649, A036650.

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;
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 + S4[T,h-1,z]z, z], n+1];
Sum[Take[CoefficientList[z^(n+1) + S5[T,h-1,z]z - S5[T,h-2,z]z - (T[h-1,z] - T[h-2,z]) (T[h-1,z]-1),z], n+1], {h,1,n/2}] + PadRight[{0,1}, n+1] (* Robert A. Russell, Sep 15 2018 *)

a(n) = A036650(n) - A036649(n).

cp's OEIS Frontend

A036650 Number of 5-valent trees with n nodes.

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