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A247081 Positive integers n such that the numerator of the harmonic mean of the nontrivial divisors of n is equal to n. 3
8, 15, 18, 21, 33, 35, 39, 45, 51, 55, 57, 63, 65, 69, 77, 81, 85, 87, 91, 93, 95, 99, 111, 115, 117, 119, 123, 128, 129, 133, 141, 143, 145, 147, 153, 155, 159, 161, 162, 171, 175, 177, 183, 185, 187, 201, 203, 205, 207, 209, 213, 215, 217, 219, 221, 235 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

No primes are in this sequence.

LINKS

Colin Barker, Table of n, a(n) for n = 1..2500

EXAMPLE

18 is a term because the nontrivial divisors of 18 are [2,3,6,9] and 4 / (1/2+1/3+1/6+1/9) = 18/5.

PROG

(PARI)

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

nontrivialdivisors(n) = d=divisors(n); vector(#d-2, k, d[k+1])

s=[]; for(n=2, 500, t=nontrivialdivisors(n); if(#t>0 && numerator(harmonicmean(t))==n, s=concat(s, n))); s

CROSSREFS

Cf. A250094, A250095.

Sequence in context: A179107 A160524 A161541 * A133157 A014544 A237610

Adjacent sequences:  A247078 A247079 A247080 * A247082 A247083 A247084

KEYWORD

nonn

AUTHOR

Colin Barker, Nov 17 2014

STATUS

approved

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Last modified November 15 08:37 EST 2019. Contains 329144 sequences. (Running on oeis4.)