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(2)*P(8) - P(10) = A085548 * A085968 - P(10) = 0.000843..., where P is the prime zeta function. - Amiram Eldar, Jul 06 2020
MATHEMATICA
f[n_]:=Sort[Last/@FactorInteger[n]]=={2, 8}; Select[Range[10^6], f]
PROG
(PARI) list(lim)=my(v=List(), t); forprime(p=2, (lim\4)^(1/8), t=p^8; forprime(q=2, sqrt(lim\t), if(p==q, next); listput(v, t*q^2))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 24 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, Jul 24 2010
STATUS
approved