OFFSET
1,2
COMMENTS
a(n) is squarefree except for n = 5, 14, 49, ... where squared prime factors are 11, 211, 479, ...
a(n)/A128646(n) is the asymptotic mean over the positive integers of the number of prime divisors that are not greater than prime(n), counted with multiplicity (cf. A007814, A169611, A356006). - Amiram Eldar, Jul 23 2022
LINKS
Eric Weisstein's World of Mathematics, Prime Sums.
FORMULA
a(n) = numerator(Sum_{k=1..n} 1/(prime(k)-1)).
MATHEMATICA
Numerator[Table[Sum[1/(Prime[i]-1), {i, 1, n}], {n, 1, 50}]]
PROG
(PARI) a(n) = numerator(sum(k=1, n, 1/(prime(k)-1))); \\ Michel Marcus, Oct 02 2016
CROSSREFS
KEYWORD
frac,nonn
AUTHOR
Alexander Adamchuk, Jul 01 2006
STATUS
approved