OFFSET
1,1
COMMENTS
a(n) is the number of fractions of denominator n which are the sum of two unit fractions: m/n = 1/r + 1/s (m and n not necessarily coprime).
LINKS
Cyril Banderier, Florian Luca, Francesco Pappalardi, Numerators of Egyptian fractions, 2019.
FORMULA
For p prime, a(p) = 2 + tau(p+1) with tau = A000005.
EXAMPLE
a(2)=4, as there are 4 fractions with denominator 4 which are the sums of 2 unit fractions: 1/2 = 1/4 + 1/4, 2/2 = 1/2 + 1/2, 3/2 = 1/1 + 1/2, 4/2 = 1/1 + 1/1.
CROSSREFS
KEYWORD
nonn
AUTHOR
Cyril Banderier, May 15 2019
STATUS
approved