OFFSET
1,1
COMMENTS
This constant is irrational (Erdős and Straus, 1971).
LINKS
Paul Erdős and Ernst G. Straus, Some number theoretic results, Pacific Journal of Mathematics, Vol. 36, No. 3 (1971), pp. 635-646.
Michael Ian Shamos, Overcounting Functions, 2011.
FORMULA
Equals Sum_{j,k>=1} 1/(j*k)! (Shamos, 2011, p. 4).
EXAMPLE
2.48106101979076269793744769639865739568689776121713...
MAPLE
with(numtheory); evalf(Sum(tau(n)/factorial(n), n = 1 .. infinity), 120)
MATHEMATICA
RealDigits[N[Sum[DivisorSigma[0, n]/n!, {n, 1, 500}], 120]][[1]]
PROG
(PARI) suminf(k=1, numdiv(k)/k!)
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Amiram Eldar, Mar 12 2024
STATUS
approved