A228810 - OEIS

%I #21 Feb 14 2021 18:34:56

%S 88,1290,9339,102619,102729,116424,116512,343594,372889,904428,

%T 1129909,1129942,1130019,1280554,1280664,2351307,12723966,12728166,

%U 12809227,12818637,12869013

%N Numbers k, excluding primes and squares of primes, such that gcd(k, numerator of H(k-1)) > 1, where the harmonic number H(j) = Sum_{i=1..j} 1/i.

%C The corresponding GCDs are given by A228811.

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Greatest_common_divisor">Greatest common divisor</a>

%o (PARI) isA000430(n)=isprime(n) || (issquare(n,&n) && isprime(n))

%o H=0;for(n=2,1e6,H+=1/(n-1); if(!isA000430(n) && gcd(n,numerator(H))>1, print1(n", "))) \\ _Charles R Greathouse IV_, Sep 04 2013

%Y Cf. A001008, A228811.

%K nonn

%O 1,1

%A _Arkadiusz Wesolowski_, Sep 04 2013

%E a(14)-a(15) from _Charles R Greathouse IV_, Sep 04 2013

%E a(16)-a(21) from _Charles R Greathouse IV_, Sep 09 2013