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A162626
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If 0 <= n <= 3 then a(n) = n(n+1)(n+2)/3, if n >= 4 then a(n) = n(n^2+5)/3.
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2
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0, 2, 8, 20, 28, 50, 82, 126, 184, 258, 350, 462, 596, 754, 938, 1150, 1392, 1666, 1974, 2318, 2700, 3122, 3586, 4094, 4648, 5250, 5902, 6606, 7364, 8178, 9050, 9982, 10976, 12034, 13158, 14350, 15612, 16946, 18354, 19838, 21400, 23042, 24766, 26574
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| One way to generalize the magic number sequence in A018226.
See also A130598 and A162630.
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FORMULA
| From Daniel Forgues, May 3, 2011: (Start)
If 0 <= n <= 3 then a(n) = 2 T_n, otherwise a(n) = 2 (T_n - t_{n-1}), where T_n is the n_th tetrahedral number, t_n the n_th triangular number.
G.f.: (2*x*(1 - 6*x^3 + 14*x^4 - 11*x^5 + 3*x^6))/(1 - x)^4, n >= 0.
(End)
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CROSSREFS
| Cf. A007290, A018226, A033547, A130598, A162518, A162519, A162521, A162522, A162523, A162524, A162525, A162630.
Sequence in context: A192153 A190640 A018226 * A137306 A110856 A048041
Adjacent sequences: A162623 A162624 A162625 * A162627 A162628 A162629
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KEYWORD
| easy,nonn
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AUTHOR
| Omar E. Pol (info(AT)polprimos.com), Jul 07 2009, Jul 13 2009
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EXTENSIONS
| Edited by N. J. A. Sloane, Jul 18 2009
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