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 A039917 Number of orderings of 1,2,...,n^2 in an n X n matrix such that each row, each column and both diagonals are increasing. 2
 1, 1, 9, 2017, 21569213, 17835527619513, 1677123511579177202174, 24742950249259362969953039657613, 75512002909758683196631913316950684079768626, 60752021865167494642984305761115275381534124800396484901989, 15991585283632910454908797943467512732011897255095362833558749286619895509557 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Alois P. Heinz, Table of n, a(n) for n = 1..14 EXAMPLE From Alois P. Heinz, Jul 23 2012: (Start) a(2) = 1:  [1, 3]            [2, 4]. a(3) = 9: [1, 4, 7]  [1, 3, 7]  [1, 2, 7]  [1, 4, 6]  [1, 3, 6] [2, 5, 8]  [2, 5, 8]  [3, 5, 8]  [2, 5, 8]  [2, 5, 8] [3, 6, 9]  [4, 6, 9]  [4, 6, 9]  [3, 7, 9]  [4, 7, 9] . [1, 2, 6]  [1, 4, 6]  [1, 3, 6]  [1, 2, 6] [3, 5, 8]  [2, 5, 7]  [2, 5, 7]  [3, 5, 7] [4, 7, 9]  [3, 8, 9]  [4, 8, 9]  [4, 8, 9]. (End) MAPLE b:= proc(l) option remember; local n; n:= nops(l); `if`({l[]}={0},       1, add(`if`((l[i]-1<>n-i or i=1 or l[i-1]-1<=n-i) and l[i]>       `if`(i=n, 0, l[i+1]), b(subsop(i=l[i]-1, l)), 0), i=1..n))     end: a:= n-> b([n\$n]): seq(a(n), n=1..8);  # Alois P. Heinz, Jul 23 2012 CROSSREFS Cf. A039622, A181191. Sequence in context: A218692 A024125 A232684 * A162140 A006945 A089825 Adjacent sequences:  A039914 A039915 A039916 * A039918 A039919 A039920 KEYWORD nonn AUTHOR EXTENSIONS One more term from Jud McCranie, Aug 09 2001 a(6)-a(13) from Alois P. Heinz, Jul 23 2012 STATUS approved

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