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A332670
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Triangle read by rows where T(n,k) is the number of length-k compositions of n whose negation is unimodal.
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15
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1, 0, 1, 0, 1, 1, 0, 1, 2, 1, 0, 1, 3, 2, 1, 0, 1, 4, 5, 2, 1, 0, 1, 5, 7, 5, 2, 1, 0, 1, 6, 11, 10, 5, 2, 1, 0, 1, 7, 15, 16, 10, 5, 2, 1, 0, 1, 8, 20, 24, 20, 10, 5, 2, 1, 0, 1, 9, 25, 36, 31, 20, 10, 5, 2, 1, 0, 1, 10, 32, 50, 50, 36, 20, 10, 5, 2, 1
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OFFSET
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0,9
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COMMENTS
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A composition of n is a finite sequence of positive integers summing to n.
A sequence of integers is unimodal if it is the concatenation of a weakly increasing and a weakly decreasing sequence.
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LINKS
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Table of n, a(n) for n=0..77.
MathWorld, Unimodal Sequence
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EXAMPLE
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Triangle begins:
1
0 1
0 1 1
0 1 2 1
0 1 3 2 1
0 1 4 5 2 1
0 1 5 7 5 2 1
0 1 6 11 10 5 2 1
0 1 7 15 16 10 5 2 1
0 1 8 20 24 20 10 5 2 1
0 1 9 25 36 31 20 10 5 2 1
0 1 10 32 50 50 36 20 10 5 2 1
0 1 11 38 67 73 59 36 20 10 5 2 1
Column n = 7 counts the following compositions:
(7) (16) (115) (1114) (11113) (111112) (1111111)
(25) (124) (1123) (11122) (211111)
(34) (133) (1222) (21112)
(43) (214) (2113) (22111)
(52) (223) (2122) (31111)
(61) (313) (2212)
(322) (2221)
(331) (3112)
(412) (3211)
(421) (4111)
(511)
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MATHEMATICA
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unimodQ[q_]:=Or[Length[q]<=1, If[q[[1]]<=q[[2]], unimodQ[Rest[q]], OrderedQ[Reverse[q]]]];
Table[Length[Select[Join@@Permutations/@IntegerPartitions[n, {k}], unimodQ[-#]&]], {n, 0, 10}, {k, 0, n}]
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CROSSREFS
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The case of partitions is A072233.
Dominated by A072704 (the non-negated version).
The strict case is A072705.
The case of constant compositions is A113704.
Row sums are A332578.
Unimodal compositions are A001523.
Unimodal normal sequences appear to be A007052.
Non-unimodal compositions are A115981.
Non-unimodal normal sequences are A328509.
Numbers whose negated unsorted prime signature is not unimodal are A332282.
Partitions whose negated run-lengths are unimodal are A332638.
Compositions whose negation is not unimodal are A332669.
Partitions whose negated 0-appended first differences are unimodal: A332728.
Cf. A011782, A107429, A227038, A332280, A332283, A332639, A332642, A332741, A332742, A332744, A332832, A332870.
Sequence in context: A256140 A321391 A244003 * A118344 A119270 A267109
Adjacent sequences: A332667 A332668 A332669 * A332671 A332672 A332673
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KEYWORD
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nonn,tabl
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AUTHOR
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Gus Wiseman, Feb 29 2020
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STATUS
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approved
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