OFFSET
1,1
COMMENTS
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((#d-2)/sum(i=2, #d-1, 1/d[i])) == 1); \\ Michel Marcus, Nov 17 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Daniel Lignon, Nov 17 2014
EXTENSIONS
a(15)-a(24) from Michel Marcus, Nov 17 2014
STATUS
approved