OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
Felix P. Muga II, Extending the Golden Ratio and the Binet-de Moivre Formula, Preprint on ResearchGate, March 2014.
Wikipedia, Hydrogen spectral series, Humphreys series.
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
a(n) = (n+6)^2 - 6^2 = n*(n + 12), n>=0.
G.f.: x*(13 - 11*x)/(1-x)^3.
a(n) = 2*n + a(n-1) + 11 (with a(0)=0). - Vincenzo Librandi, Nov 17 2010
a(0)=0, a(1)=13, a(2)=28, a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). - Harvey P. Dale, May 24 2012
Sum_{n>=1} 1/a(n) = 86021/332640 = 0.258600... via Sum_{n>=0} 1/((n+x)(n+y)) = (psi(x)-psi(y))/(x-y). - R. J. Mathar, Jul 14 2012
E.g.f.: x*(13 + x)*exp(x). - G. C. Greubel, Jul 29 2016
Sum_{n>=1} (-1)^(n+1)/a(n) = 18107/332640. - Amiram Eldar, Jan 15 2021
MATHEMATICA
Table[ n(n + 12), {n, 0, 50}] (* Robert G. Wilson v, Jul 14 2005 *)
LinearRecurrence[{3, -3, 1}, {0, 13, 28}, 50] (* Harvey P. Dale, May 24 2012 *)
PROG
(PARI) a(n)=n*(n+12) \\ Charles R Greathouse IV, Sep 24 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eugene McDonnell (eemcd(AT)mac.com), Nov 04 2004
EXTENSIONS
More terms from Robert G. Wilson v, Jul 14 2005
STATUS
approved