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A000772
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E.g.f. exp(tan(x) + sec(x) - 1).
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3
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1, 1, 2, 6, 23, 107, 583, 3633, 25444, 197620, 1684295, 15618141, 156453857, 1683050189, 19344093070, 236497985706, 3063827565763, 41916787157011, 603799270943519, 9132945141812301, 144708157060239704
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| The number of elevated increasing binary trees. There is no restriction on the outdegree at the root. - Wenjin Woan (wjwoan(AT)hotmail.com), Jan 09 2008
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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
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CROSSREFS
| Sequence in context: A125273 A130908 A200404 * A200405 A200403 A113226
Adjacent sequences: A000769 A000770 A000771 * A000773 A000774 A000775
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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