So a(n) = n/2 if n == 0 (mod 4); n otherwise. Don't forget to mark this as multiplicative, with a(p^e) = 2^e if p = 2, e <= 1; 2^(e-1) if p = 2, e >= 2; p^e otherwise. ----- No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1204 / Virus Database: 1435/3468 - Release Date: 02/25/11