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 A015220 Even tetrahedral numbers. 1
 4, 10, 20, 56, 84, 120, 220, 286, 364, 560, 680, 816, 1140, 1330, 1540, 2024, 2300, 2600, 3276, 3654, 4060, 4960, 5456, 5984, 7140, 7770, 8436, 9880, 10660, 11480, 13244, 14190, 15180, 17296, 18424, 19600, 22100, 23426, 24804, 27720, 29260 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Sum_{n>=0} 1/a(n) = 3/2*(1-log(2)). - Ant King Oct 19 2012 LINKS FORMULA Contribution from Ant King, Oct 19 2012: (Start) a(n) = a(n-1) + 3*a(n-3) - 3*a(n-4) - 3*a(n-6) + 3*a(n-7) + a(n-9) - a(n-10) a(n) = 64 + 3*a(n-3) - 3*a(n-6) + a(n-9) G.f. 2*(2+3*x+5*x^2+12*x^3+5*x^4+3*x^5+2*x^6) / ((1-x)^4*(1+x+x^2)^3). (End) MATHEMATICA LinearRecurrence[{1, 0, 3, -3, 0, -3, 3, 0, 1, -1}, {4, 10, 20, 56, 84, 120, 220, 286, 364, 560}, 41] (* Ant King, Oct 19 2012 *) Select[Table[(Times@@(n+{0, 1, 2}))/6, {n, 60}], EvenQ] (* Harvey P. Dale, Jan 22 2013 *) CROSSREFS Cf. A000292. Sequence in context: A056412 A032275 A220828 * A047199 A038065 A038422 Adjacent sequences:  A015217 A015218 A015219 * A015221 A015222 A015223 KEYWORD nonn,easy AUTHOR EXTENSIONS More terms from Erich Friedman. STATUS approved

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