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A033462
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Exponential (or "EXP") transform of squares A000290.
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0
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1, 1, 5, 22, 125, 836, 6277, 52396, 479593, 4757680, 50738921, 577894604, 6990138685, 89376020800, 1203182518189, 16995248375116, 251135780602193, 3871961504546624, 62141329025501905, 1035979079450355532
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| 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 3,2011
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FORMULA
| E.g.f.: exp(exp(x)(x+x^2))
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MATHEMATICA
| Range[0, 20]! CoefficientList[Series[Exp[Exp[x](x+x^2)], {x, 0, 20}], x]
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CROSSREFS
| Sequence in context: A159596 A020077 A203265 * A111154 A028561 A009638
Adjacent sequences: A033459 A033460 A033461 * A033463 A033464 A033465
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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