OFFSET
0,2
COMMENTS
Nonnegative k such that k/9 + 1 is a square. - Bruno Berselli, Apr 10 2018
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..5000
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
a(n) = 9*n*(n+2).
a(n) = a(n-1) + 9*A144396(n) for n > 0.
From Elmo R. Oliveira, Nov 29 2024: (Start)
G.f.: 9*x*(3 - x)/(1-x)^3.
E.g.f.: 9*x*(3 + x)*exp(x).
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n >= 3. (End)
MATHEMATICA
Table[9 n (n + 2), {n, 0, 60}] (* Harvey P. Dale, Feb 20 2011 *)
72*Binomial[Range[0, 60]/2 +1, 2] (* G. C. Greubel, Dec 17 2025 *)
PROG
(PARI) a(n)=9*n*(n+2) \\ Charles R Greathouse IV, Jun 17 2017
(Magma) A147651:= func< n | 9*n*(n+2) >; // G. C. Greubel, Dec 17 2025
(Python) def A147651(n): return 9*n*(n+2) # G. C. Greubel, Dec 17 2025
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paul Curtz, Nov 09 2008
EXTENSIONS
More terms from Vincenzo Librandi, Nov 26 2010
Terms a(35) onward added by G. C. Greubel, Dec 17 2025
STATUS
approved
