OFFSET
0,3
COMMENTS
If a(n,k) is the number of permutations of 1..n with no adjacent pair summing to n+k, then a(n,k) = a(n,k+1) for n+k even. [proved by William Keith]
FORMULA
k = 5; a(n,k) = Sum_{j=0..m} (-2)^j*binomial(m,j)*(n-j)! where m = max(0, floor((n-k+1)/2)). [Max Alekseyev, on the Sequence Fans Mailing List]
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 26 2010
EXTENSIONS
More terms from Alois P. Heinz, Jan 09 2017
STATUS
approved