21977357

Appears in sequences

• a(n) = floor(Sum_{k=0..n} k!/2), or floor( A003422(n+1)/2 ).at n=11A014288
• Numerator of probability that a permutation of elements of some subset of set {1,2,...,n} is a permutation of elements of some set of the form 1..k, k <= n.at n=10A293458