

A173849


Number of permutations of 1..n with no adjacent pair summing to n + 9.


0



1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 2903040, 32659200, 333849600, 4470681600, 55244851200, 855496857600, 12362073292800, 216999220838400, 3584572069478400, 70276861528473600, 1305169212624076800, 28251875803447296000, 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 = 9; m = max(0, floor((nk+1)/2)); a(n,k) = Sum_{j=0..m} (2)^j * binomial(m,j)*(nj)!.


CROSSREFS

Sequence in context: A276843 A273696 A177280 * A154657 A179361 A179368
Adjacent sequences: A173846 A173847 A173848 * A173850 A173851 A173852


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



