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 A178977 a(n) = (3*n+2)*(3*n+5)/2. 3
 5, 20, 44, 77, 119, 170, 230, 299, 377, 464, 560, 665, 779, 902, 1034, 1175, 1325, 1484, 1652, 1829, 2015, 2210, 2414, 2627, 2849, 3080, 3320, 3569, 3827, 4094, 4370, 4655, 4949, 5252, 5564, 5885, 6215, 6554, 6902, 7259, 7625, 8000, 8384, 8777, 9179 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Companion to A145910. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..10000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = a(n-1)+6+9*n. a(n) = A178971(3*n+2). a(n) = A145910(n)+3+3*n = A145910(n)+A008585(n+1). a(n) = A168233(n+1)*A168300(n+1). G.f.: (-5-5*x+x^2)/(x-1)^3. [Adapted to the offset by Bruno Berselli, Apr 14 2011] a(n) = 3*a(n-1)-3*a(n-2)+a(n-3). - Harvey P. Dale, Apr 19 2013 From Amiram Eldar, Mar 10 2022: (Start) Sum_{n>=0} 1/a(n) = 1/3. Sum_{n>=0} (-1)^n/a(n) = 4*Pi/(9*sqrt(3)) - 1/3 - 4*log(2)/9. (End) MAPLE A178977:=n->(3*n+2)*(3*n+5)/2: seq(A178977(n), n=0..50); # Wesley Ivan Hurt, Oct 23 2014 MATHEMATICA f[n_] := (3 n + 2) (3 n + 5)/2; Array[f, 45, 0] LinearRecurrence[{3, -3, 1}, {5, 20, 44}, 50] (* Harvey P. Dale, Apr 19 2013 *) PROG (Magma) [n*(n+3)/2: n in [2..135 by 3]]; // Bruno Berselli, Apr 14 2011 (PARI) a(n)=(3*n+2)*(3*n+5)/2 \\ Charles R Greathouse IV, Jun 17 2017 CROSSREFS Cf. A008585, A145910, A168233, A168300, A178971, A235332. Sequence in context: A031304 A363695 A228168 * A061188 A033429 A168011 Adjacent sequences: A178974 A178975 A178976 * A178978 A178979 A178980 KEYWORD nonn,easy AUTHOR Paul Curtz, Jan 02 2011 STATUS approved

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Last modified November 29 13:49 EST 2023. Contains 367445 sequences. (Running on oeis4.)