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Search: id:A002941
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| A002941 |
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Arrays of dumbbells.
(Formerly M4396 N1852)
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+0
11
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| 1, 7, 29, 94, 263, 667, 1577, 3538, 7622, 15900, 32314, 64274, 125561, 241569, 458715, 861242, 1601081, 2950693, 5396209, 9801012, 17692092, 31759800, 56727588, 100861716, 178585489, 314995915, 553650761, 969967510, 1694235803
(list; graph; listen)
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OFFSET
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1,2
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REFERENCES
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I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, Wiley, N.Y., 1983,(2.3.14).
R. C. Grimson, Exact formulas for 2 x n arrays of dumbbells, J. Math. Phys., 15 (1974), 214-216.
R. B. McQuistan and S. J. Lichtman, Exact recursion relation for 2 x N arrays of dumbbells, J. Math. Phys., 11 (1970), 3095-3099.
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FORMULA
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G.f.: (1+x)^2/(1-x-x^2)^3/(1-x)^2.
a(n)=2*a(n-1)-a(n-3)+A002940(n)+A002940(n-1)
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CROSSREFS
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Cf. A046741, A002940, A002889, A055608, A062123-A062127.
Adjacent sequences: A002938 A002939 A002940 this_sequence A002942 A002943 A002944
Sequence in context: A055798 A002664 A042609 this_sequence A102485 A049349 A124828
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KEYWORD
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nonn,easy
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AUTHOR
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njas
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EXTENSIONS
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More terms from Henry Bottomley (se16(AT)btinternet.com), Jun 02 2000
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