OFFSET
2,7
COMMENTS
a(n) = 0 when n = 2, any prime of the form 4k+1 with k >= 1 and any product of these without repetition, e.g. 2x5x17.
LINKS
G. C. Greubel, Table of n, a(n) for n = 2..10000
MATHEMATICA
Table[Sum[Floor[k^2/n], {k, 1, n - 1}] - Floor[(n - 1)*(n - 2)/3], {n, 2, 100}] (* G. C. Greubel, May 12 2016 *)
PROG
(PARI) a(n) = sum(j=1, n-1, j^2\n) - ((n-1)*(n-2))\3 \\ Michel Marcus, Jun 21 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Christopher Hunt Gribble, Oct 13 2009
EXTENSIONS
Corrected and enhanced by Christopher Hunt Gribble, Dec 01 2009
STATUS
approved