

A173848


Number of permutations of 1..n with no adjacent pair summing to n + 8.


0



1, 1, 2, 6, 24, 120, 720, 5040, 40320, 282240, 2903040, 26853120, 333849600, 3802982400, 55244851200, 745007155200, 12362073292800, 192275074252800, 3584572069478400, 63107717389516800, 1305169212624076800, 25641537378199142400, 582386191297118208000
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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.


LINKS

Table of n, a(n) for n=0..22.


FORMULA

k = 8; m = max(0, floor((nk+1)/2)); a(n,k) = Sum_{j=0..m} (2)^j * binomial(m,j)*(nj)!.


CROSSREFS

Sequence in context: A276842 A273695 A177279 * A154656 A179354 A179360
Adjacent sequences: A173845 A173846 A173847 * A173849 A173850 A173851


KEYWORD

nonn


AUTHOR

R. H. Hardin, Feb 26 2010


EXTENSIONS

Comment proved by William Keith, formula from Max Alekseyev, on the Sequence Fans Mailing List
More terms from Alois P. Heinz, Jan 09 2017


STATUS

approved



