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Search: id:A053307
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| A053307 |
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Number of nonnegative integer 2 X 2 matrices with sum of elements equal to n, under row and column permutations. |
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+0
10
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| 1, 1, 4, 5, 11, 14, 24, 30, 45, 55, 76, 91, 119, 140, 176, 204, 249, 285, 340, 385, 451, 506, 584, 650, 741, 819, 924, 1015, 1135, 1240, 1376, 1496, 1649, 1785, 1956, 2109, 2299, 2470, 2680, 2870, 3101, 3311, 3564, 3795, 4071, 4324, 4624, 4900, 5225, 5525
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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An interleaved sequence of pyramidal and polygonal numbers: a(2n)= A006527(n+1), a(2n+1)=A000330(n+1) - Paul Barry (pbarry(AT)wit.ie), Mar 17 2003
Contribution from Ramasamy Chandramouli (thedavinci(AT)gmail.com), Jan 17 2009: (Start)
a(n) is also the number of solutions to the equation XOR(x1, x2, ..., xn) = 0
such that each xi is a 2-bit binary number and xi >= xj for i >= j.
For example, a(2) = 4 since (x1, x2) = { (00, 00), (01, 01), (10, 10), (11, 11) } (End)
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FORMULA
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G.f.: (x^2-x+1)/((1-x^2)^2*(1-x)^2).
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CROSSREFS
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Cf. A081283, A081284.
Sequence in context: A084812 A050018 A125577 this_sequence A076065 A066898 A118143
Adjacent sequences: A053304 A053305 A053306 this_sequence A053308 A053309 A053310
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KEYWORD
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easy,nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)eunet.rs), Mar 05 2000
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