Infected and death percentages per age group in Brazil as of 21th March, 2020.

Si(0) is just multiplication of corresponding age group population percentage (second column in Table 1) by the total population N, discounted the corresponding number of infected in the age group. Ri(0) = 0 as at the time of writing it was not a significant data (just 6 recovered individuals). It is a common assumption for early stages of the infection, as is the case in Brazil and in many other countries.