OFFSET
1,1
REFERENCES
From a puzzle proposed by Marc LeBrun.
FORMULA
Sum_{n>=1} 1/a(n) = (4/7) * (zeta(2)*zeta(3)/zeta(6)) - 8/9 = 0.221737646437... . - Amiram Eldar, Sep 19 2023
MATHEMATICA
f[p_, e_] := NextPrime[p, 2]^(e + 1); a[1] = 9; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Sep 19 2023 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
EXTENSIONS
More terms from David W. Wilson
STATUS
approved