What is the infinite sum of regular numbers?

Question

What and is the infinite sum of regular numbers? $\sum 1/r$ where r is regular number. Upto 10 digit accurate. Thanks

Edit. http://oeis.org/A003592

Answer 1

It seems that the question is referring to numbers of the form $2^m 5^n$. In that case, $$ \sum_{r=2^m5^n} \frac1r = \sum_{m=0}^\infty \sum_{n=0}^\infty \frac1{2^m5^n} = \sum_{m=0}^\infty \frac1{2^m} \sum_{n=0}^\infty \frac1{5^n} = 2\cdot\frac54 = \frac52. $$ To 10-digit accuracy, the answer is 2.5000000000.