OFFSET
1,1
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
Will Nicholes, Prime Signatures
FORMULA
Sum_{n>=1} 1/a(n) = P(3)*P(6) - P(9) = A085541 * A085966 - A085969 = 0.000978..., where P is the prime zeta function. - Amiram Eldar, Jul 06 2020
a(n) = A054753(n)^3. - R. J. Mathar, May 05 2023
MATHEMATICA
f[n_]:=Sort[Last/@FactorInteger[n]]=={3, 6}; Select[Range[10^6], f]
PROG
(PARI) list(lim)=my(v=List(), t); forprime(p=2, (lim\8)^(1/6), t=p^6; forprime(q=2, (lim\t)^(1/3), if(p==q, next); listput(v, t*q^3))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 24 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, Jul 24 2010
STATUS
approved