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A245747 Number of identity trees with n nodes where the maximal outdegree (branching factor) equals 2. 2
1, 2, 5, 10, 21, 42, 87, 178, 371, 773, 1630, 3447, 7346, 15712, 33790, 72922, 158020, 343494, 749101, 1638102, 3591723, 7893801, 17387930, 38379199, 84875595, 188036829, 417284180, 927469844, 2064465340, 4601670624, 10270463564, 22950838754, 51346678940 (list; graph; refs; listen; history; text; internal format)
OFFSET

4,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 4..1000

FORMULA

a(n) = A063895(n+1)-1.

MAPLE

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

      `if`(i<1, 0, add(binomial(b(i-1$2, k$2), j)*

       b(n-i*j, i-1, t-j, k), j=0..min(t, n/i))))

    end:

a:= n-> b(n-1$2, 2$2) -b(n-1$2, 1$2):

seq(a(n), n=4..60);

CROSSREFS

Column k=2 of A244523.

Sequence in context: A280148 A215410 A279668 * A032283 A266248 A027437

Adjacent sequences:  A245744 A245745 A245746 * A245748 A245749 A245750

KEYWORD

nonn

AUTHOR

Joerg Arndt and Alois P. Heinz, Jul 31 2014

STATUS

approved

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Last modified May 21 17:10 EDT 2019. Contains 323444 sequences. (Running on oeis4.)