1,2

Harmonic mean of the divisors of number n is rational number b(n) = n*A000005(n) / A000203(n) = A099377(n) / A099378(n). a(n) = 1 for infinitely many n. a(n) = 1 for numbers from A001599: a(A001599(n)) = 1. a(n) = 1 iff A099378(n) = 1.

Table of n, a(n) for n=1..35.

For n = 4; b(4) = 12/7, a(n) = 7 because b(7) = 7/4; 12/7 * 7/4 = 3 (integer).

Sequence in context: A248054 A329421 A100985 * A230710 A265009 A021757

Adjacent sequences: A176799 A176800 A176801 * A176803 A176804 A176805

nonn

Jaroslav Krizek, Apr 26 2010

approved