OFFSET
1,2
COMMENTS
Multiplicative closure of A000043. - Charles R Greathouse IV, Feb 21 2013
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{n>=1} 1/a(n) = Product_{p in A000043} p/(p-1) = 5.7838... - Amiram Eldar, Sep 27 2020
EXAMPLE
10 = 2 * 5 is a term since both 2 and 5 are Mersenne exponents (A000043).
MATHEMATICA
p = Join[{1}, MersennePrimeExponent @ Range[12]]; Select[Range[p[[-1]]], AllTrue[FactorInteger[#][[;; , 1]], MemberQ[p, #] &] &] (* Amiram Eldar, Sep 27 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from James A. Sellers, Apr 22 2000
STATUS
approved