OFFSET
0,5
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..10000
Mircea Merca, Inequalities and Identities Involving Sums of Integer Functions J. Integer Sequences, Vol. 14 (2011), Article 11.9.1.
Index entries for linear recurrences with constant coefficients, signature (3,-3,1,0,0,0,0,0,1,-3,3,-1).
FORMULA
a(n) = Sum_{k=0..n} floor(k^2/9).
a(n) = round((2*n^3 + 3*n^2 - 15*n - 9)/54).
a(n) = round((2*n^3 + 3*n^2 - 15*n - 8)/54).
a(n) = floor((2*n^3 + 3*n^2 - 15*n + 18)/54).
a(n) = ceiling((2*n^3 + 3*n^2 - 15*n - 34)/54).
a(n) = a(n-9) + (n-4)^2 + 4, n > 8.
G.f.: x^3*(x+1)*(x^2 - x + 1)^2/((x-1)^4*(x^2 + x + 1)*(x^6 + x^3 + 1)). [Colin Barker, Oct 26 2012]
EXAMPLE
a(6) = 8 = 0 + 0 + 0 + 1 + 1 + 2 + 4.
MAPLE
a:= n-> round((2*n^3+3*n^2-15*n-9)/54): seq (a(n), n=0..50);
MATHEMATICA
Accumulate[Floor[Range[0, 50]^2/9]] (* or *) LinearRecurrence[{3, -3, 1, 0, 0, 0, 0, 0, 1, -3, 3, -1}, {0, 0, 0, 1, 2, 4, 8, 13, 20, 29, 40, 53}, 60] (* Harvey P. Dale, Jan 10 2020 *)
PROG
(Magma) [Round((2*n^3+3*n^2-15*n-9)/54): n in [0..60]]; // Vincenzo Librandi, Jun 25 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Mircea Merca, Nov 19 2010
STATUS
approved