OFFSET
1,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..239
FORMULA
a(n) = Sum_{j=1..n} binomial(n,j) * A374980(n-j). - Alois P. Heinz, Aug 05 2024
EXAMPLE
a(3) = 16: The 15 permutations with one stable pair (see A375222) and the starting configuration [1, 1, 2, 2, 3, 3].
PROG
(PARI) a375223(n) = {my (p=vector(2*n, i, 1+(i-1)\2), m=0); forperm (p, q, for (j=1, n, if (q[2*j-1]==j && q[2*j]==j, m++; break))); m}
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Aug 05 2024
EXTENSIONS
a(8) onwards from Alois P. Heinz, Aug 05 2024
STATUS
approved