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A338526
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Triangle read by rows: T(n,k) is the number of permutations of k elements from [1..n] without consecutive adjacent values.
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5
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1, 1, 1, 1, 2, 0, 1, 3, 2, 0, 1, 4, 6, 4, 2, 1, 5, 12, 18, 20, 14, 1, 6, 20, 48, 90, 124, 90, 1, 7, 30, 100, 272, 582, 860, 646, 1, 8, 42, 180, 650, 1928, 4386, 6748, 5242, 1, 9, 56, 294, 1332, 5110, 15912, 37566, 59612, 47622, 1, 10, 72, 448, 2450, 11604, 46250, 148648, 360642, 586540, 479306
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OFFSET
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0,5
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LINKS
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EXAMPLE
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n\k 0 1 2 3 4 5 6 7 8
0 1
1 1 1
2 1 2 0
3 1 3 2 0
4 1 4 6 4 2
5 1 5 12 18 20 14
6 1 6 20 48 90 124 90
7 1 7 30 100 272 582 860 646
8 1 8 42 180 650 1928 4386 6748 5242
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PROG
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(PARI) isok(s, p) = {for (i=1, #s-1, if (abs(s[p[i+1]] - s[p[i]]) == 1, return (0)); ); return (1); }
T(n, k) = {my(nb = 0); forsubset([n, k], s, for(i=1, k!, if (isok(s, numtoperm(k, i)), nb++); ); ); nb; } \\ Michel Marcus, Nov 17 2020
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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