The sample of RaCl_{2} isolated by marie Curie contained 91 mg of radium-226, with a half-life of 1600 years. What was the decay rate in s^{-1} of her asmple at the time it was isolated?

I know I have to use the decay rate = lambda times N. So, then I converted the 91 mg of radium to atoms so that I could find N to be 2.4245 x 10^{20} which seemed to be a bit high to me. So, then I took that number times the decay constant and got 3.6368 x 10^{15}

I just wanted to make sure that I did this right. Thanks!