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A357189
Number of integer partitions of n with the same length as alternating sum.
25
1, 1, 0, 0, 1, 1, 1, 2, 2, 4, 3, 5, 6, 9, 9, 13, 16, 23, 23, 34, 37, 54, 54, 78, 84, 120, 121, 170, 182, 252, 260, 358, 379, 517, 535, 725, 764, 1030, 1064, 1427, 1494, 1992, 2059, 2733, 2848, 3759, 3887, 5106, 5311, 6946, 7177, 9345, 9701, 12577, 12996, 16788
OFFSET
0,8
COMMENTS
A partition of n is a weakly decreasing sequence of positive integers summing to n.
The alternating sum of a sequence (y_1,...,y_k) is Sum_i (-1)^(i-1) y_i.
EXAMPLE
The a(4) = 1 through a(13) = 9 partitions:
31 311 42 322 53 333 64 443 75 553
421 5111 432 5221 542 5331 652
531 6211 641 6222 751
51111 52211 6321 52222
62111 7311 53311
711111 62221
63211
73111
7111111
MATHEMATICA
ats[y_]:=Sum[(-1)^(i-1)*y[[i]], {i, Length[y]}];
Table[Length[Select[IntegerPartitions[n], Length[#]==ats[#]&]], {n, 0, 30}]
CROSSREFS
For product equal to sum we have A001055, compositions A335405.
For product instead of length we have A004526, compositions A114220.
The version for compositions is A357182, ranked by A357184.
For sum equal to twice alternating sum we have A357189 (this sequence).
These partitions are ranked by A357486.
The reverse version is A357487, ranked by A357485.
A000041 counts partitions, strict A000009.
A025047 counts alternating compositions.
A103919 counts partitions by alternating sum, full triangle A344651.
A357136 counts compositions by alternating sum, full triangle A097805.
Sequence in context: A058723 A329436 A182577 * A241450 A189675 A248746
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 30 2022
STATUS
approved