OFFSET
1,1
COMMENTS
Essentially a duplicate of A059100.
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..5000
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
a(n) = (1/5) * A027578(n-1).
a(n) = 2*n + a(n-1) + 1 (with a(1)=6). - Vincenzo Librandi, Nov 16 2010
a(n) = A059100(n+1). - Reinhard Zumkeller, Mar 21 2008
a(n) = A010000(n+1) for n >= 1. - Georg Fischer, Nov 02 2018
From Amiram Eldar, Sep 14 2022: (Start)
Sum_{n>=1} 1/a(n) = Pi * coth(sqrt(2)*Pi)/(2*sqrt(2)) - 7/12.
Sum_{n>=1} (-1)^(n+1)/a(n) = cosech(sqrt(2)*Pi)*Pi/(2*sqrt(2)) + 1/12. (End)
From G. C. Greubel, Feb 03 2024: (Start)
G.f.: (3 - 3*x + 2*x^2)/(1-x)^3.
E.g.f.: (3 + 3*x + x^2)*exp(x). (End)
MAPLE
MATHEMATICA
Table[n^2+2n+3, {n, 50}] (* or *) LinearRecurrence[{3, -3, 1}, {6, 11, 18}, 50] (* Harvey P. Dale, Aug 05 2015 *)
PROG
(PARI) a(n)=n^2+2*n+3 \\ Charles R Greathouse IV, Oct 16 2015
(Magma) [(n+1)^2+2: n in [1..60]]; // G. C. Greubel, Feb 03 2024
(SageMath) [n^2+2*n+3 for n in range(1, 61)] # G. C. Greubel, Feb 03 2024
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Ralf Stephan, Jan 03 2005
STATUS
approved