OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
a(n) = A166146(n)+1.
a(n) = a(n-1)+7*n = 3*a(n-1) -3*a(n-2) +a(n-3).
G.f.: x*(-2-10*x+5*x^2)/(x-1)^3.
E.g.f.: (7/2)*((x^2 + 2*x - 5)*exp(x) + 5). - G. C. Greubel, May 01 2016
Sum_{n>=1} 1/a(n) = 1/5 + (2*Pi/sqrt(329))*tan(sqrt(47/7)*Pi/2). - Amiram Eldar, Feb 20 2023
MATHEMATICA
Table[7 n (n + 1)/2 - 5, {n, 100}] (* or *) CoefficientList[Series[(- 2 - 10 x + 5 x^2) / (x - 1)^3, {x, 0, 50}], x] (* Vincenzo Librandi, Sep 13 2013 *)
LinearRecurrence[{3, -3, 1}, {2, 16, 37}, 50] (* G. C. Greubel, May 01 2016 *)
PROG
(Magma) [7*n*(n+1)/2-5: n in [1..50]]; // Vincenzo Librandi, Sep 13 2013
(PARI) a(n)=7*n*(n+1)/2-5 \\ Charles R Greathouse IV, May 02 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Oct 08 2009
EXTENSIONS
Definition replaced by polynomial, A-number corrected, formulas added by R. J. Mathar, Oct 12 2009
STATUS
approved