OFFSET
0,11
COMMENTS
A sequence of positive integers is unimodal if it is the concatenation of a weakly increasing and a weakly decreasing sequence.
LINKS
MathWorld, Unimodal Sequence
EXAMPLE
The a(8) = 1 through a(13) = 10 partitions:
(3221) (4221) (5221) (4331) (4332) (5332)
(32221) (6221) (5331) (6331)
(42221) (7221) (8221)
(322211) (43221) (43321)
(52221) (53221)
(322221) (62221)
(422211) (332221)
(422221)
(522211)
(3222211)
MATHEMATICA
unimodQ[q_]:=Or[Length[q]<=1, If[q[[1]]<=q[[2]], unimodQ[Rest[q]], OrderedQ[Reverse[q]]]]
Table[Length[Select[IntegerPartitions[n], !unimodQ[-Length/@Split[#]]&]], {n, 0, 30}]
CROSSREFS
The version for normal sequences is A328509.
The non-negated complement is A332280.
The non-negated version is A332281.
The complement is counted by A332638.
The case that is not unimodal either is A332640.
The Heinz numbers of these partitions are A332642.
The generalization to run-lengths of compositions is A332727.
Unimodal compositions are A001523.
Non-unimodal permutations are A059204.
Non-unimodal compositions are A115981.
Compositions whose negation is not unimodal are A332669.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Feb 25 2020
STATUS
approved