A332748 The number of permutations of {1,1,1,2,2,2,...,n,n,n} such that each triple of k's (k=1..n) is equally spaced with b(k) other elements in between and b(1) >= b(2) >= ... >= b(n).
1, 1, 4, 18, 124, 738, 7464, 55890, 668778, 7030210, 90713844, 1054221258, 18597735744, 242795838520
Offset: 0
Examples
n = 1 case: | | b(1) -----+-----------+------ 1 | [1, 1, 1] | [0] * . n = 2 case: | | b(1),b(2) -----+--------------------+---------- 1 | [2, 2, 2, 1, 1, 1] | [0, 0] 2 | [2, 1, 2, 1, 2, 1] | [1, 1] 3 | [1, 2, 1, 2, 1, 2] | [1, 1] 4 | [1, 1, 1, 2, 2, 2] | [0, 0] . n = 3 case: | | b(1),b(2),b(3) -----+-----------------------------+--------------- 1 | [3, 3, 3, 2, 2, 2, 1, 1, 1] | [0, 0, 0] 2 | [3, 3, 3, 2, 1, 2, 1, 2, 1] | [1, 1, 0] 3 | [3, 3, 3, 1, 2, 1, 2, 1, 2] | [1, 1, 0] 4 | [3, 3, 3, 1, 1, 1, 2, 2, 2] | [0, 0, 0] 5 | [3, 2, 1, 3, 2, 1, 3, 2, 1] | [2, 2, 2] 6 | [3, 1, 2, 3, 1, 2, 3, 1, 2] | [2, 2, 2] 7 | [1, 3, 3, 3, 1, 2, 2, 2, 1] | [3, 0, 0] 8 | [2, 3, 1, 2, 3, 1, 2, 3, 1] | [2, 2, 2] 9 | [1, 3, 2, 1, 3, 2, 1, 3, 2] | [2, 2, 2] 10 | [2, 1, 3, 2, 1, 3, 2, 1, 3] | [2, 2, 2] 11 | [1, 2, 3, 1, 2, 3, 1, 2, 3] | [2, 2, 2] 12 | [2, 2, 2, 3, 3, 3, 1, 1, 1] | [0, 0, 0] 13 | [1, 1, 1, 3, 3, 3, 2, 2, 2] | [0, 0, 0] 14 | [1, 2, 2, 2, 1, 3, 3, 3, 1] | [3, 0, 0] 15 | [2, 2, 2, 1, 1, 1, 3, 3, 3] | [0, 0, 0] 16 | [2, 1, 2, 1, 2, 1, 3, 3, 3] | [1, 1, 0] 17 | [1, 2, 1, 2, 1, 2, 3, 3, 3] | [1, 1, 0] 18 | [1, 1, 1, 2, 2, 2, 3, 3, 3] | [0, 0, 0] * (strongly decreasing)
Crossrefs
Extensions
a(10)-a(13) from Max Alekseyev, Sep 26 2023