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A173850 Number of permutations of 1..n with no adjacent pair summing to n+10. 0

%I

%S 1,1,2,6,24,120,720,5040,40320,362880,3628800,32659200,399168000,

%T 4470681600,64186214400,855496857600,14073067008000,216999220838400,

%U 4018570511155200,70276861528473600,1445722935681024000,28251875803447296000,638889942904012800000

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

%C 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.

%F k = 10; m = max(0, floor((n-k+1)/2)); a(n,k) = Sum_{j=0..m} (-2)^j * binomial(m,j)*(n-j)!.

%K nonn

%O 0,3

%A _R. H. Hardin_, Feb 26 2010

%E Comment proved by William Keith, formula from _Max Alekseyev_, on the Sequence Fans Mailing List

%E More terms from _Alois P. Heinz_, Jan 09 2017

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Last modified January 24 10:24 EST 2020. Contains 331193 sequences. (Running on oeis4.)