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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 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.)