OFFSET
3,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 3..200
Eric Weisstein's World of Mathematics, Inverse Erf
FORMULA
a(n) = A197365(n,1).
a(n) ~ c * d^n * n! * n, where d = 1/A240885 = 1/(sqrt(2) * InverseErf(sqrt(2/Pi))) = 0.78397693120354749... and c = 0.679554202696108785... . - Vaclav Kotesovec, Oct 29 2015
EXAMPLE
a(3) = 1: 132.
a(4) = 8: 1243, 1324, 1423, 1432, 2143, 2431, 3142, 4132.
a(5) = 54: 12354, 12435, 12534, ..., 52431, 53142, 54132.
a(6) = 368: 123465, 123546, 123645, ..., 652431, 653142, 654132.
a(7) = 2649: 1234576, 1234657, 1234756, ..., 7652431, 7653142, 7654132.
MAPLE
b:= proc(u, o, t, c) option remember; `if`(u+o=0, c, add(
b(u-j, o+j-1, 0, c+`if`(j<=t, 1, 0)), j=`if`(c=1, t, 0)
+1..u) +add(b(u+j-1, o-j, j-1, c), j=1..o))
end:
a:= n-> b(n, 0$3):
seq(a(n), n=3..30);
MATHEMATICA
Drop[Coefficient[CoefficientList[Series[1/(1 - (Sqrt[Pi/2]*Erfi[(Sqrt[u-1]*x) / Sqrt[2]])/Sqrt[u-1]), {x, 0, 25}], x] * Range[0, 25]!, u], 3] (* Vaclav Kotesovec, Oct 29 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 28 2015
STATUS
approved