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A335562 Number of unlabelled unary-binary trees with n nodes such that every node with two children has children of different subtree sizes. 0
1, 1, 1, 3, 5, 13, 29, 71, 165, 421, 1029, 2647, 6593, 17241, 43801, 115555, 297513, 791337, 2062737, 5516755, 14497373, 38994597, 103269053, 278921927, 742950845, 2014648253, 5396210357, 14677306503, 39477832745, 107701409665, 290871580345, 795431700707, 2155140605137 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Table of n, a(n) for n=1..33.

FORMULA

a(1) = 1, a(n) = a(n-1) + Sum_{k=1..n-2} (a(k)*a(n-k-1)*[k != n-k-1]).

PROG

(PARI) lista(nn) = {my(va = vector(nn)); va[1] = 1; for (n=2, nn, va[n] = va[n-1] + sum(k=1, n-2, if (k != n-k-1, va[k]*va[n-k-1])); ); va; } \\ Michel Marcus, Jun 14 2020

CROSSREFS

Cf. A000992.

Sequence in context: A238216 A067932 A168314 * A106666 A124791 A147046

Adjacent sequences:  A335559 A335560 A335561 * A335563 A335564 A335565

KEYWORD

nonn

AUTHOR

Marcel K. Goh, Jun 14 2020

STATUS

approved

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Last modified October 31 05:06 EDT 2020. Contains 338098 sequences. (Running on oeis4.)