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A000772 E.g.f. exp(tan(x) + sec(x) - 1). 4
1, 1, 2, 6, 23, 107, 583, 3633, 25444, 197620, 1684295, 15618141, 156453857, 1683050189, 19344093070, 236497985706, 3063827565763, 41916787157011, 603799270943519, 9132945141812301, 144708157060239704, 2396568154933265024, 41403636316192616995 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

The number of elevated increasing binary trees. There is no restriction on the outdegree at the root. - Wenjin Woan, Jan 09 2008

LINKS

T. D. Noe, Table of n, a(n) for n = 0..100

FORMULA

a(n)=sum(k=1..n, A147315(n-1,k-1)), n>0, a(0)=1. [From Vladimir Kruchinin, Mar 10 2011]

a(n) = D^n(exp(x)) evaluated at x = 0, where D is the operator (1+x+x^2/2!)*d/dx. Cf. A000110 and A094198. See also A185422. - Peter Bala, Nov 25 2011

MATHEMATICA

nn = 25; Range[0, nn]! CoefficientList[Series[Exp[Tan[x] + Sec[x] - 1], {x, 0, nn}], x] (* T. D. Noe, Jun 20 2012 *)

CROSSREFS

Sequence in context: A277176 A130908 A200404 * A200405 A200403 A113226

Adjacent sequences:  A000769 A000770 A000771 * A000773 A000774 A000775

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified February 20 11:03 EST 2018. Contains 299385 sequences. (Running on oeis4.)