OFFSET
1,2
COMMENTS
Row 2 of the array A211785.
LINKS
Bruno Berselli, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (3, -2, -2, 3, -1).
FORMULA
a(n) = 3*a(n-1)-2*a(n-2)-2*a(n-3)+3*a(n-4)-a(n-5).
G.f.: x*(1+9*x+6*x^2+2*x^3)/((1+x)*(1-x)^4). [Bruno Berselli, May 06 2012]
a(n) = floor(3*n^3/2) = (6*n^3+(-1)^n-1)/4. [Bruno Berselli, May 06 2012]
MATHEMATICA
f[n_, m_] := Sum[Floor[n^3/k], {k, 1, m}]
t = Table[f[n, 2], {n, 1, 90}]
FindLinearRecurrence[t]
LinearRecurrence[{3, -2, -2, 3, -1}, {1, 12, 40, 96, 187}, 38] (* Ray Chandler, Aug 02 2015 *)
PROG
(Magma) [n^3+Floor(n^3/2): n in [1..38]]; // Bruno Berselli, May 06 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Apr 20 2012
STATUS
approved