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Search: id:A067589
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| 1, 5, 7, 15, 35, 51, 57, 77, 117, 145, 155, 187, 247, 287, 301, 345, 425, 477, 495, 551, 651, 715, 737, 805, 925, 1001, 1027, 1107, 1247, 1335, 1365, 1457, 1617, 1717, 1751, 1855, 2035, 2147, 2185, 2301, 2501, 2625, 2667, 2795, 3015, 3151, 3197, 3337
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OFFSET
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1,2
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COMMENT
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Apparently groups of two odd pentagonal numbers (A000326, A014632) followed by two odd 2nd pentagonal numbers (A005449), which leads to the conjectured generating function x*(x^2+4*x+1)*(x^4-2*x^3+4*x^2-2*x+1)/((x^2+1)^2*(1-x)^3). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 26 2009]
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FORMULA
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The terms are exactly the odd pentagonal numbers; that is, they are all the odd numbers of the form n(3n-1)/2 where n is an integer. - James A. Sellers (sellersj(AT)math.psu.edu), Jun 09 2007
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CROSSREFS
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Cf. A067588, A000009.
Sequence in context: A072022 A003429 A076860 this_sequence A059613 A116048 A120282
Adjacent sequences: A067586 A067587 A067588 this_sequence A067590 A067591 A067592
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KEYWORD
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easy,nonn
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AUTHOR
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Naohiro Nomoto (n_nomoto(AT)yabumi.com), Jan 31 2002
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EXTENSIONS
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Corrected by T. D. Noe (noe(AT)sspectra.com), Oct 25 2006
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