A225963 Number of permutations of [n] having exactly 2 strong fixed blocks.

1, 5, 25, 134, 815, 5657, 44549, 394266, 3883182, 42174500, 500942458, 6460077110, 89875729761, 1341559805867, 21382747361727, 362402701510514, 6507348542427217, 123394642353693319, 2463866954996239829, 51670868533003154264, 1135456889195715187948

Offset: 4

Author

Alois P. Heinz, May 22 2013

Keywords

• nonn

Comments

See A186373 for the definition of strong fixed blocks.

Links

• Alois P. Heinz, Table of n, a(n) for n = 4..450

Crossrefs

Column k=2 of A186373.

Formula

a(n) ~ n! / n^2. - Vaclav Kotesovec, Aug 29 2014