A332725 Heinz numbers of integer partitions whose negated first differences are not unimodal.

90, 126, 180, 198, 234, 252, 270, 306, 342, 350, 360, 378, 396, 414, 450, 468, 504, 522, 525, 540, 550, 558, 594, 612, 630, 650, 666, 684, 700, 702, 720, 738, 756, 774, 792, 810, 825, 828, 846, 850, 882, 900, 910, 918, 936, 950, 954, 975, 990, 1008, 1026, 1044

Offset

1,1

Comments

A sequence of positive integers is unimodal if it is the concatenation of a weakly increasing and a weakly decreasing sequence.

The Heinz number of an integer partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k). This gives a bijective correspondence between positive integers and integer partitions.

Links

Table of n, a(n) for n=1..52.

MathWorld, Unimodal Sequence

Gus Wiseman, Sequences counting and ranking integer partitions by the differences of their successive parts.

Example

The sequence of terms together with their prime indices begins:
    90: {1,2,2,3}
   126: {1,2,2,4}
   180: {1,1,2,2,3}
   198: {1,2,2,5}
   234: {1,2,2,6}
   252: {1,1,2,2,4}
   270: {1,2,2,2,3}
   306: {1,2,2,7}
   342: {1,2,2,8}
   350: {1,3,3,4}
   360: {1,1,1,2,2,3}
   378: {1,2,2,2,4}
   396: {1,1,2,2,5}
   414: {1,2,2,9}
   450: {1,2,2,3,3}
   468: {1,1,2,2,6}
   504: {1,1,1,2,2,4}
   522: {1,2,2,10}
   525: {2,3,3,4}
   540: {1,1,2,2,2,3}
For example, 350 is the Heinz number of (4,3,3,1), with negated first differences (1,0,2), which is not unimodal, so 350 is in the sequence.

Mathematica

primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
unimodQ[q_]:=Or[Length[q]<=1, If[q[[1]]<=q[[2]], unimodQ[Rest[q]], OrderedQ[Reverse[q]]]];
Select[Range[1000], !unimodQ[Differences[primeMS[#]]]&]

Crossrefs

The complement is too full.

The enumeration of these partitions by sum is A332284.

The version where the last part is taken to be 0 is A332832.

Non-unimodal permutations are A059204.

Non-unimodal compositions are A115981.

Non-unimodal normal sequences are A328509.

Partitions with non-unimodal run-lengths are A332281.

Heinz numbers of partitions with non-unimodal run-lengths are A332282.

Heinz numbers of partitions with weakly increasing differences are A325360.

Cf. A001523, A007052, A240026, A332280, A332283, A332285, A332286, A332288, A332294, A332579, A332639, A332642.

Sequence in context: A025371 A025362 A114826 * A253385 A332831 A103653

Adjacent sequences: A332722 A332723 A332724 * A332726 A332727 A332728

Keyword

nonn

Author

Gus Wiseman, Feb 26 2020

Status

approved