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Search: id:A122823
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| A122823 |
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Triangle read by rows: T(n,k) = count of increasing runs in two concatenated k-permutations of [n]. |
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+0
2
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| 2, 7, 11, 15, 96, 132, 26, 378, 2088, 2664, 40, 1040, 12960, 66240, 80640, 57, 2325, 51600, 594000, 2894400, 3412800, 77, 4536, 157500, 3225600, 35380800, 166924800, 192326400, 100, 8036, 402192, 12877200, 251193600, 2667168000, 12294374400
(list; table; graph; listen)
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OFFSET
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1,1
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FORMULA
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T(n,k) = ((k+1) - (n-1)/2n) * Permute(n,k)^2
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EXAMPLE
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Triangle begins:
2
7 11
15 96 132
Take the 2-permutations of [2] namely 12 and 21 and form all possible strings that are concatenations of two of these permutations. These are 1212,1221,2112,2121 with 2,3,3,3 increasing runs respectively. T(2,2) = 2+3+3+3 = 11.
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CROSSREFS
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Column 1 = T(n, 1) = A005449, Second pentagonal numbers: n*(3n+1)/2.
Sequence in context: A018308 A001960 A140491 this_sequence A063289 A049635 A079140
Adjacent sequences: A122820 A122821 A122822 this_sequence A122824 A122825 A122826
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KEYWORD
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easy,nonn,tabl
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AUTHOR
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David J. Scambler (dscambler(AT)bmm.com), Oct 29 2006
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