A250097 - OEIS

A250097

Denominator of the harmonic mean of the prime factors, without multiplicity, of n.

1, 1, 1, 1, 5, 1, 1, 1, 7, 1, 5, 1, 9, 4, 1, 1, 5, 1, 7, 5, 13, 1, 5, 1, 15, 1, 9, 1, 31, 1, 1, 7, 19, 6, 5, 1, 21, 8, 7, 1, 41, 1, 13, 4, 25, 1, 5, 1, 7, 10, 15, 1, 5, 8, 9, 11, 31, 1, 31, 1, 33, 5, 1, 9, 61, 1, 19, 13, 59, 1, 5, 1, 39, 4, 21, 9, 71, 1, 7

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OFFSET

2,5

LINKS

Colin Barker, Table of n, a(n) for n = 2..1000

EXAMPLE

a(6) = 5 because the distinct prime factors of 6 are [2,3] and 2 / (1/2+1/3) = 12/5.

PROG

(PARI)

harmonicmean(v) = #v / sum(k=1, #v, 1/v[k])

a(n) = denominator(harmonicmean(factorint(n)~[1, ]))

vector(100, n, a(n+1))