OFFSET
0,4
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
KEYWORD
nonn
AUTHOR
Geoffrey Critzer, May 11 2012
STATUS
approved