OFFSET
1,2
LINKS
Mathematics Stack Exchange, What is sum ?, 2015.
FORMULA
Equals 1/4 + Sum_{j>=2} (j-1) * (-1)^j * (zeta(j)^2 - 1).
Equals Sum_{k>=1} d(k)/(k+1)^2, where d(k) is the number of divisors of k (A000005).
EXAMPLE
1.39020754344374685423356578449853168588839698392360363639250826208529335...
PROG
(PARI) default(realprecision, 120); 1/4 + sumalt(j=2, (j-1)*(-1)^j*(zeta(j)^2 - 1))
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Vaclav Kotesovec, Jun 26 2020
STATUS
approved