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 A261902 Irregular triangle read by rows: T(n,m) = number of permutations of {1, 2, ..., n} which form arithmetic progressions modulo m (n>=1, 1<=m<=n+2). 0

%I

%S 1,1,1,2,2,2,2,6,2,6,2,2,24,8,4,8,4,2,120,12,8,4,20,2,2,720,72,48,8,8,

%T 12,6,2,5040,144,48,16,8,4,42,4,2,40320,1152,144,128,16,8,12,23,6,2,

%U 362880,2880,1296,96,64,16,8,8,54,4,2

%N Irregular triangle read by rows: T(n,m) = number of permutations of {1, 2, ..., n} which form arithmetic progressions modulo m (n>=1, 1<=m<=n+2).

%D F. Luca, A. O. Munagi, The Number Of Permutations Which Form Arithmetic Progressions Modulo m, Annals of the Alexandru Ioan Cuza University, 2014, DOI: 10.2478/aicu-2014-0053

%e Triangle begins:

%e 1,1,1,

%e 2,2,2,2,

%e 6,2,6,2,2,

%e 24,8,4,8,4,2,

%e 120,12,8,4,20,2,2,

%e 720,72,48,8,8,12,6,2,

%e 5040,144,48,16,8,4,42,4,2,

%e 40320,1152,144,128,16,8,12,23,6,2,

%e 362880,2880,1296,96,64,16,8,8,54,4,2,

%e ...

%Y T(n,n) = A002618(n).

%K nonn,tabf

%O 1,4

%A _N. J. A. Sloane_, Sep 07 2015

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Last modified April 19 06:30 EDT 2019. Contains 322237 sequences. (Running on oeis4.)