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A085001
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a(n) = (3n+1)(3n+4).
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1
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4, 28, 70, 130, 208, 304, 418, 550, 700, 868, 1054, 1258, 1480, 1720, 1978, 2254, 2548, 2860, 3190, 3538, 3904, 4288, 4690, 5110, 5548, 6004, 6478, 6970, 7480, 8008, 8554, 9118, 9700, 10300, 10918, 11554, 12208, 12880, 13570, 14278, 15004
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| 1/4 + 1/28 + 1/70 +... = 1/3; 1/4 + 1/28 + 1/70 +... n terms = n/(3*n + 1). [Jolley]. - Gary W. Adamson (qntmpkt(AT)yahoo.com), Jan 03 2007
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REFERENCES
| L. B. W. Jolley, "Summation of Series", Dover Publications, 1961, p. 38
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LINKS
| Index entries for sequences related to linear recurrences with constant coefficients, signature (3,-3,1).
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FORMULA
| Sum(0<=k<n) 3/a(k) = 3n/(3n+1); sum(k>=0) 3/a(k) = 1.
G.f.: 2(2+8x-x^2)/(1-x)^3. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Sep 17 2008]
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CROSSREFS
| Sequence in context: A197542 A203280 A085024 * A153784 A030117 A005634
Adjacent sequences: A084998 A084999 A085000 * A085002 A085003 A085004
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KEYWORD
| nonn,easy
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AUTHOR
| Gary W. Adamson (qntmpkt(AT)yahoo.com), Jun 17 2003
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EXTENSIONS
| Edited by Don Reble (djr(AT)nk.ca), Nov 13 2005
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