

A247079


Numbers for which the harmonic mean of nontrivial divisors is an integer and which are not a square of prime numbers.


2



345, 1050, 1645, 4386, 6489, 8041, 13026, 23881, 88473, 115957, 255041, 342637, 377201, 1497517, 2132021, 2428489, 3256261, 3847001, 4114285, 4646101, 5054221, 6816865, 7218641, 7587901, 13384681, 14872837, 17897737, 20901553, 23807821, 25863653, 28207957
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OFFSET

1,1


COMMENTS

That's the numbers which are in A247078 and not in A001248.
a(149) >= 2*10^11.  Hiroaki Yamanouchi, Nov 20 2014


LINKS

Daniel Lignon and Hiroaki Yamanouchi, Table of n, a(n) for n = 1..148 (terms a(1)a(40) from Daniel Lignon)


EXAMPLE

345 is not the square of a prime number and the nontrivial divisors of 345 are [3,5,15,23,69,115]. Their harmonic mean is 6/(1/3+1/5+1/15+1/23+1/69+1/115)=9.


PROG

(PARI) isok(n) = !(issquare(n) && isprime(sqrtint(n))) && (d=divisors(n)) && (#d > 2) && (denominator((#d2)/sum(i=2, #d1, 1/d[i])) == 1); \\ Michel Marcus, Nov 17 2014


CROSSREFS

Cf. A001599 (harmonic numbers), A247078.
Sequence in context: A116347 A063370 A095963 * A236731 A138043 A048904
Adjacent sequences: A247076 A247077 A247078 * A247080 A247081 A247082


KEYWORD

nonn


AUTHOR

Daniel Lignon, Nov 17 2014


EXTENSIONS

a(15)a(24) from Michel Marcus, Nov 17 2014


STATUS

approved



