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A351012
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Number of even-length integer partitions y of n such that y_i = y_{i+1} for all even i.
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11
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1, 0, 1, 1, 3, 3, 5, 6, 9, 10, 13, 16, 21, 24, 29, 35, 43, 50, 60, 70, 83, 97, 113, 132, 156, 178, 206, 239, 275, 316, 365, 416, 477, 545, 620, 706, 806, 912, 1034, 1173, 1326, 1496, 1691, 1902, 2141, 2410, 2704, 3034, 3406, 3808, 4261, 4765, 5317, 5932, 6617
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OFFSET
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0,5
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LINKS
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EXAMPLE
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The a(2) = 1 through a(8) = 9 partitions:
(11) (21) (22) (32) (33) (43) (44)
(31) (41) (42) (52) (53)
(1111) (2111) (51) (61) (62)
(3111) (2221) (71)
(111111) (4111) (2222)
(211111) (3221)
(5111)
(311111)
(11111111)
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MATHEMATICA
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Table[Length[Select[IntegerPartitions[n], EvenQ[Length[#]]&&And@@Table[#[[i]]==#[[i+1]], {i, 2, Length[#]-1, 2}]&]], {n, 0, 30}]
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CROSSREFS
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The ordered version (compositions) is A027383(n-2).
The version for unequal parts appears to be A122134, any length A122135.
This is the even-length case of A351003.
Requiring inequalities at odd positions gives A351007, any length A351006.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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