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A033488
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a(n) = n*(n+1)*(n+2)*(n+3)/6.
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15
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0, 4, 20, 60, 140, 280, 504, 840, 1320, 1980, 2860, 4004, 5460, 7280, 9520, 12240, 15504, 19380, 23940, 29260, 35420, 42504, 50600, 59800, 70200, 81900, 95004, 109620, 125860, 143840, 163680, 185504, 209440
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OFFSET
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0,2
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COMMENTS
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LINKS
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FORMULA
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G.f.: 2*x/(1-x)*W(0), where W(k) = 1 + 1/( 1 - x*(k+2)*(k+4)/(x*(k+2)*(k+4) + (k+1)*(k+2)/W(k+1) )) ); (continued fraction). - Sergei N. Gladkovskii, Aug 24 2013
Sum_{n>=1} 1/a(n) = 1/3.
Sum_{n>=1} (-1)^(n+1)/a(n) = 8*log(2) - 16/3. (End)
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MAPLE
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MATHEMATICA
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PROG
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CROSSREFS
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Convolution of the oblong numbers with the odd numbers: A008911.
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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