

A173850


Number of permutations of 1..n with no adjacent pair summing to n+10.


0



1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 32659200, 399168000, 4470681600, 64186214400, 855496857600, 14073067008000, 216999220838400, 4018570511155200, 70276861528473600, 1445722935681024000, 28251875803447296000, 638889942904012800000
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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 = 10; m = max(0, floor((nk+1)/2)); a(n,k) = Sum_{j=0..m} (2)^j * binomial(m,j)*(nj)!.


CROSSREFS

Sequence in context: A276844 A273697 A177281 * A154658 A179369 A267390
Adjacent sequences: A173847 A173848 A173849 * A173851 A173852 A173853


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



