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A132768
a(n) = n*(n + 26).
7
0, 27, 56, 87, 120, 155, 192, 231, 272, 315, 360, 407, 456, 507, 560, 615, 672, 731, 792, 855, 920, 987, 1056, 1127, 1200, 1275, 1352, 1431, 1512, 1595, 1680, 1767, 1856, 1947, 2040, 2135, 2232, 2331, 2432, 2535, 2640, 2747, 2856, 2967, 3080, 3195, 3312, 3431
OFFSET
0,2
LINKS
FORMULA
a(n) = n*(n + 26).
a(n) = 2*n + a(n-1) + 25, with a(0)=0. - Vincenzo Librandi, Aug 03 2010
From Amiram Eldar, Jan 16 2021: (Start)
Sum_{n>=1} 1/a(n) = H(26)/26 = A001008(26)/A102928(26) = 34395742267/232016584800, where H(k) is the k-th harmonic number.
Sum_{n>=1} (-1)^(n+1)/a(n) = 18051406831/696049754400. (End)
From G. C. Greubel, Mar 13 2022: (Start)
G.f.: x*(27 - 25*x)/(1-x)^3.
E.g.f.: x*(27 + x)*exp(x). (End)
MATHEMATICA
Table[n(n+26), {n, 0, 50}] (* or *) LinearRecurrence[{3, -3, 1}, {0, 27, 56}, 50] (* Harvey P. Dale, Dec 15 2018 *)
PROG
(PARI) a(n)=n*(n+26) \\ Charles R Greathouse IV, Jun 17 2017
(Sage) [n*(n+26) for n in (0..50)] # G. C. Greubel, Mar 13 2022
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Aug 28 2007
STATUS
approved