OFFSET
1,2
COMMENTS
Row 3 of the array A211783.
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,1,0,-1,-1,1).
FORMULA
a(n) = a(n-1)+a(n-2)-a(n-4)-a(n-5)+a(n-6) for n>=7.
G.f.: x*(1+6*x+8*x^2+6*x^3+x^4)/((1-x)^3*(1+2*x+2*x^2+x^3)). - Bruno Berselli, May 06 2012
a(n) = (66*n^2 + 9*(-1)^n - 17 - 4*A061347(n))/36. - Stefano Spezia, Nov 23 2023
MATHEMATICA
f[n_, m_] := Sum[Floor[n^2/k], {k, 1, m}]
t = Table[f[n, 3], {n, 1, 90}]
FindLinearRecurrence[t]
LinearRecurrence[{1, 1, 0, -1, -1, 1}, {1, 7, 16, 29, 45, 66}, 46] (* Ray Chandler, Aug 02 2015 *)
PROG
(Magma) [&+[Floor(n^2/k): k in [1..3]]: n in [1..46]]; // Bruno Berselli, May 06 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Apr 20 2012
STATUS
approved