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A003510
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An equivalence relation on permutations.
(Formerly M1510)
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1
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1, 1, 2, 5, 17, 67, 352, 1969, 13295, 97619, 848354, 7647499, 82862683, 897904165, 11226063188, 146116260203, 2089038231953, 30230018309161, 508450431515290, 8318618236423861, 154636109939564681, 2896102013935844771, 59056861862689101272
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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REFERENCES
| N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
R. P. Stanley, Problem 5932, Amer. Math. Monthly, 82 (1975), 86-87.
R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.18.
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FORMULA
| E.g.f.: exp ( Sum_{i=1..inf} x^i / i*phi(i) ), phi = Euler phi function (A000010).
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MAPLE
| with(numtheory); exp(add(x^n/(n*phi(n)), n=1..31));
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MATHEMATICA
| max = 22; f[x_] := Exp[ Sum[ x^k/(k*EulerPhi[k]), {k, 1, max}]]; CoefficientList[ Series[ f[x], {x, 0, max}], x]*Range[0, max]! (* From Jean-François Alcover, Oct 12 2011 *)
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CROSSREFS
| Sequence in context: A104082 A166474 A054769 * A051625 A056098 A027361
Adjacent sequences: A003507 A003508 A003509 * A003511 A003512 A003513
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KEYWORD
| nonn,easy,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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