OFFSET
1,1
COMMENTS
The values of a(n) for 1 <= n <= 14 are primes, a(15) = 1081 = 23*47.
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
From G. C. Greubel, Oct 19 2017: (Start)
G.f.: x*(31 - 24*x + x^2)/(1 - x)^3.
E.g.f.: (1 + 30*x + 3*x^2)*exp(x) - 1. (End)
Sum_{n>=1} 1/a(n) = tan(sqrt(239/3)*Pi/2)*Pi/sqrt(717) - 2643017/2948761. - Amiram Eldar, Jan 31 2023
MATHEMATICA
Table[3*n^2 + 27*n + 1, {n, 100}]
PROG
(PARI) a(n)=3*n^2+27*n+1 \\ Charles R Greathouse IV, Jun 17 2017
(Magma) [3*n^2 + 27*n + 1: n in [1..25]]; // G. C. Greubel, Oct 19 2017
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Joao da Silva (zxawyh66(AT)yahoo.com), Sep 16 2005
EXTENSIONS
Edited by Arkadiusz Wesolowski, Oct 11 2011
STATUS
approved