A372834 - OEIS

A372834

a(n) is the numerator of Sum_{d|n, d < sqrt(n)} 1/d.

0, 1, 1, 1, 1, 3, 1, 3, 1, 3, 1, 11, 1, 3, 4, 3, 1, 11, 1, 7, 4, 3, 1, 25, 1, 3, 4, 7, 1, 61, 1, 7, 4, 3, 6, 25, 1, 3, 4, 39, 1, 2, 1, 7, 23, 3, 1, 9, 1, 17, 4, 7, 1, 2, 6, 53, 4, 3, 1, 49, 1, 3, 31, 7, 6, 2, 1, 7, 4, 129, 1, 19, 1, 3, 23, 7, 8, 2, 1, 83

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,6

LINKS

Table of n, a(n) for n=1..80.

FORMULA

Numerators of coefficients in expansion of Sum_{k>=1} x^(k*(k+1)) / (k * (1 - x^k)).

EXAMPLE

0, 1, 1, 1, 1, 3/2, 1, 3/2, 1, 3/2, 1, 11/6, 1, 3/2, 4/3, 3/2, 1, 11/6, ...

MATHEMATICA

nmax = 80; CoefficientList[Series[Sum[x^(k (k + 1))/(k (1 - x^k)), {k, 1, nmax}], {x, 0, nmax}], x] // Numerator // Rest

PROG