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A033462
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Exponential (or "EXP") transform of squares A000290.
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13
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1, 1, 5, 22, 125, 836, 6277, 52396, 479593, 4757680, 50738921, 577894604, 6990138685, 89376020800, 1203182518189, 16995248375116, 251135780602193, 3871961504546624, 62141329025501905, 1035979079450355532, 17907209511611407141, 320387246623657457056, 5924125441456047522005
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OFFSET
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0,3
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COMMENTS
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a(n) is the number of ways to select an ordered pair from each equivalence class in each equivalence relation on {1,2,...,n}. - Geoffrey Critzer, Oct 03 2011
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LINKS
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FORMULA
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E.g.f.: exp(exp(x)*(x+x^2)).
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MAPLE
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a:= proc(n) option remember; `if`(n=0, 1,
add(binomial(n-1, j-1)*j^2*a(n-j), j=1..n))
end:
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MATHEMATICA
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Range[0, 20]! CoefficientList[Series[Exp[Exp[x](x+x^2)], {x, 0, 20}], x]
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PROG
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(PARI)
N=33; x='x+O('x^N);
egf=exp(x*(1+x)*exp(x));
Vec(serlaplace(egf))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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