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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 (list; graph; refs; listen; history; text; internal format)
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((n-k+1)/2)); a(n,k) = Sum_{j=0..m} (-2)^j * binomial(m,j)*(n-j)!.

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

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Last modified February 24 01:16 EST 2020. Contains 332195 sequences. (Running on oeis4.)