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A103831
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For even n, a(n)=n(n+1), for odd n, a(n)=2n+1
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1
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0, 3, 6, 7, 20, 11, 42, 15, 72, 19, 110, 23, 156, 27, 210, 31, 272, 35, 342, 39, 420, 43, 506, 47, 600, 51, 702, 55, 812, 59, 930, 63, 1056, 67, 1190, 71, 1332, 75, 1482, 79, 1640, 83, 1806, 87, 1980, 91, 2162, 95, 2352, 99, 2550, 103, 2756, 107, 2970, 111, 3192, 115
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| First the product then the sum of two successive integers.
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FORMULA
| G.f.: (6*x^5+3*x^4-18*x^3-10*x^2+20*x+7) / (1-x)^3*(1+x)^3.
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EXAMPLE
| a(4)=4*5=20, a(5)=5+6=11.
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MATHEMATICA
| Flatten[Table[{i + i + 1, (i + 1)(i + 2)}, {i, 1, 99, 2}]]
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CROSSREFS
| Cf. A103832.
Sequence in context: A072773 A130049 A056703 * A106357 A088101 A050867
Adjacent sequences: A103828 A103829 A103830 * A103832 A103833 A103834
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KEYWORD
| nonn
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AUTHOR
| Zak Seidov (zakseidov(AT)yahoo.com), Feb 17 2005, Feb 18 2005
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EXTENSIONS
| Edited by N. J. A. Sloane (njas(AT)research.att.com), Aug 29 2008 at the suggestion of R. J. Mathar
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