A338914 - OEIS

A338914

Number of integer partitions of n of even length whose greatest multiplicity is at most half their length.

1, 0, 0, 1, 1, 2, 3, 4, 6, 9, 11, 16, 23, 29, 39, 53, 69, 90, 118, 150, 195, 249, 315, 398, 506, 629, 789, 982, 1219, 1504, 1860, 2277, 2798, 3413, 4161, 5051, 6137, 7406, 8948, 10765, 12943, 15503, 18571, 22153, 26432, 31432, 37352, 44268, 52444, 61944, 73141

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OFFSET

0,6

COMMENTS

These are also integer partitions that can be partitioned into not necessarily distinct edges (pairs of distinct parts). For example, (3,3,2,2) can be partitioned as {{2,3},{2,3}}, so is counted under a(10), but (4,2,2,2) and (4,2,1,1,1,1) cannot be partitioned into edges. The multiplicities of such a partition form a multigraphical partition (A209816, A320924).

LINKS

Table of n, a(n) for n=0..50.

Eric Weisstein's World of Mathematics, Graphical partition.

FORMULA

A027187(n) = a(n) + A096373(n).

EXAMPLE

The a(3) = 1 through a(10) = 11 partitions:

(21) (31) (32) (42) (43) (53) (54) (64)

(41) (51) (52) (62) (63) (73)

(2211) (61) (71) (72) (82)

(3211) (3221) (81) (91)

(3311) (3321) (3322)

(4211) (4221) (4321)

(4311) (4411)

(5211) (5221)

(222111) (5311)

(6211)

(322111)

MATHEMATICA

Table[Length[Select[IntegerPartitions[n], EvenQ[Length[#]]&&Max@@Length/@Split[#]<=Length[#]/2&]], {n, 0, 30}]

CROSSREFS

A096373 counts the complement in even-length partitions.

A320911 gives the Heinz numbers of these partitions.

A339560 is the strict case.

A339562 counts factorizations of the same type.

A000070 counts non-multigraphical partitions of 2n, ranked by A339620.

A000569 counts graphical partitions, ranked by A320922.

A001358 lists semiprimes, with squarefree case A006881.

A002100 counts partitions into squarefree semiprimes.

A058696 counts partitions of even numbers, ranked by A300061.

A209816 counts multigraphical partitions, ranked by A320924.

A320656 counts factorizations into squarefree semiprimes.

A320921 counts connected graphical partitions, ranked by A320923.

A339617 counts non-graphical partitions of 2n, ranked by A339618.

A339655 counts non-loop-graphical partitions of 2n, ranked by A339657.

A339656 counts loop-graphical partitions, ranked by A339658.

The following count partitions of even length and give their Heinz numbers:

- A027187 has no additional conditions (A028260).

- A096373 cannot be partitioned into strict pairs (A320891).

- A338915 cannot be partitioned into distinct pairs (A320892).

- A338916 can be partitioned into distinct pairs (A320912).

- A339559 cannot be partitioned into distinct strict pairs (A320894).

- A339560 can be partitioned into distinct strict pairs (A339561).

Cf. A001055, A001221, A005117, A007717, A030229, A320655, A322353, A338899, A338903.

Sequence in context: A198394 A035947 A371839 * A048249 A370843 A377151

Adjacent sequences: A338911 A338912 A338913 * A338915 A338916 A338917

KEYWORD

nonn

AUTHOR

Gus Wiseman, Dec 09 2020

STATUS

approved