OFFSET
1,2
COMMENTS
Number of nonempty subsets of divisors of n = A100587(n).
FORMULA
Let a, b, c, ..., k be all divisors of n; a(n) = (a+1) * (b+1) * ... * (k+1) - 1.
a(p) = 2p+1, a(p^2) = 2(p+1)(p^2+1) - 1.
a(n) = A020696(n) - 1.
EXAMPLE
For n = 2^2 = 4; divisors of 4: {1, 2, 4}; nonempty subsets of divisors of n: {1}, {2}, {4}, {1, 2}, {1, 4}, {2, 4}, {1, 2, 4}; sum of products of elements of subsets = 1 + 2 + 4 + 2 + 4 + 8 + 8 = 29 = (1+1) * (2+1) * (4+1) - 1.
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Sep 20 2013
STATUS
approved