A211371 - OEIS

A211371

The number of indecomposable n-permutations that have only cycles of length 3 or less.

0, 1, 1, 3, 7, 29, 131, 585, 3083, 17089, 97987, 607977, 3926731, 26344001, 185908739, 1358432937, 10279616891, 80819893393, 655374770131, 5482528852761, 47329769940331, 420061520283617, 3832533793409027, 35926633641149865, 345280194806563931

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OFFSET

0,4

LINKS

Table of n, a(n) for n=0..24.

FORMULA

G.f.: 1-1/A(x) where A(x) is the o.g.f. for A057693.

EXAMPLE

a(4) = 7 because we have: 2431, 3241, 3412, 4132, 4213, 4231, 4321.

MATHEMATICA

nn = 20; a = x + x^2/2 + x^3/3; b = Total[Range[0, nn]! CoefficientList[Series[Exp[a], {x, 0, nn}], x]* x^Range[0, nn]]; CoefficientList[Series[1 - 1/b, {x, 0, nn}], x]

CROSSREFS

Cf. A057693, A003319, A140456.

Sequence in context: A217576 A173280 A141477 * A361436 A302157 A294383

Adjacent sequences: A211368 A211369 A211370 * A211372 A211373 A211374

KEYWORD

nonn

AUTHOR

Geoffrey Critzer, May 11 2012

STATUS

approved