A372835 - OEIS

A372835

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

1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 6, 1, 2, 3, 2, 1, 6, 1, 4, 3, 2, 1, 12, 1, 2, 3, 4, 1, 30, 1, 4, 3, 2, 5, 12, 1, 2, 3, 20, 1, 1, 1, 4, 15, 2, 1, 4, 1, 10, 3, 4, 1, 1, 5, 28, 3, 2, 1, 20, 1, 2, 21, 4, 5, 1, 1, 4, 3, 70, 1, 8, 1, 2, 15, 4, 7, 1, 1, 40

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OFFSET

1,6

LINKS

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

FORMULA

Denominators 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] // Denominator // Rest

PROG