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A106236 Triangle of the numbers of different forests with m rooted trees having distinct orders. 2
1, 1, 0, 2, 1, 0, 4, 2, 0, 0, 9, 6, 0, 0, 0, 20, 13, 2, 0, 0, 0, 48, 37, 4, 0, 0, 0, 0, 115, 86, 17, 0, 0, 0, 0, 0, 286, 239, 46, 0, 0, 0, 0, 0, 0, 719, 577, 142, 8, 0, 0, 0, 0, 0, 0, 1842, 1607, 367, 18, 0, 0, 0, 0, 0, 0, 0, 4766, 4025, 1136, 76, 0, 0, 0, 0, 0, 0, 0, 0, 12486, 11185, 2945, 248, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

a(n) = 0 if and only if n < m + (((1+m)*m - 1)^2 -1)/8, where m is the number of trees in the forests counted by a(n).

LINKS

Alois P. Heinz, Rows n = 1..141, flattened

FORMULA

a(n) = sum over the partitions of N: 1K1 + 2K2 + ... + NKN, with exactly m distinct parts, of Product_{i=1..N}binomial(A000081(i)+Ki-1, Ki). Because all the multiplicities of the parts of the considered partitions are 1, or 0, we can simplify the formula to a(n)= sum over the partitions of N with exactly m distinct parts, of Product_{i=1..N}A000081(i). (Naturally, we do not consider the parts with multiplicity 0.)

G.f.: Product_{k>0} (1 + y*A000081(k)*x^k). - Vladeta Jovovic, May 14 2005

EXAMPLE

a(3) = 0 because m = 2 and (see comments) 3 < (2 + 3).

a(4) > 0 because m = 1. Note that (((1+m)*m - 1)^2 -1)/8 = 0, if m = 1. It is clear that n >= m.

MAPLE

with(numtheory):

g:= proc(n) option remember; `if`(n<=1, n, (add(add(

      d*g(d), d=divisors(j))*g(n-j), j=1..n-1))/(n-1))

    end:

b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,

      expand(add(x^j*b(n-i*j, i-1)*binomial(g(i)+j-1, j),

      j=0..min(1, n/i)))))

    end:

T:= n-> (p-> seq(coeff(p, x, i), i=1..n))(b(n$2)):

seq(T(n), n=1..14);  # Alois P. Heinz, Jun 25 2014

MATHEMATICA

g[n_] := g[n] = If[n <= 1, n, (Sum[Sum[d*g[d], {d, Divisors[j]}]*g[n-j], {j, 1, n-1}])/(n-1)]; b[n_, i_] := b[n, i] = If[n == 0, 1, If[i<1, 0, Expand[Sum[x^j*b[n - i*j, i-1]*Binomial[g[i]+j-1, j], {j, 0, Min[1, n/i]}]]]]; T[n_] := Function[{p}, Table[Coefficient[p, x, i], {i, 1, n}]][b[n, n]]; Table[T[n], {n, 1, 14}] // Flatten (* Jean-Fran├žois Alcover, Feb 23 2015, after Alois P. Heinz *)

CROSSREFS

Cf. A000081, A106234.

Sequence in context: A166555 A136329 A122073 * A270640 A139136 A122792

Adjacent sequences:  A106233 A106234 A106235 * A106237 A106238 A106239

KEYWORD

nonn,tabl

AUTHOR

Washington Bomfim, Apr 28 2005

STATUS

approved

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Last modified July 11 07:39 EDT 2020. Contains 335626 sequences. (Running on oeis4.)