OFFSET
1,4
COMMENTS
If n = Product (p_j^k_j) is the standard prime power decomposition of n, there is a set of size A001221(n) which contains the divisors which are largest powers of primes, {p_1^k_1, p_2^k_2, ..., p_j^k_j}. a(n) sums all the divisors not in this set. If p, q, ..., z are distinct primes, k are natural numbers (A000027), p^k prime powers (A000961), the following formulas hold: a(p) = 1. a(pq) = pq+1. a(pq...z) = (p+1)* (q+1)* ... *(z+1) - (p+q+ ...+z). a(p^k) = (p^k-1)/(p-1).
LINKS
Nathaniel Johnston, Table of n, a(n) for n = 1..10000
EXAMPLE
For n = 12, set of prime-power-factor divisors of 12: {3, 4}, set of non-(prime-power-factor) divisors on 12: {1, 2, 6, 12}. a(12) = 1+2+6+12=21.
MAPLE
A008475 := proc(n) add( op(1, d)^op(2, d), d= ifactors(n)[2] ) ; end proc:
seq(A167515(n), n=1..80) ; # R. J. Mathar, Dec 21 2010
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Dec 15 2010
STATUS
approved