Answer based on context:

After the death of his older half-brother and financial support, Carl Erik, when Lars Levi was only a teenager, Laestadius mourned the deaths of his mother in 1824, his dad in 1832, and his younger brother Petrus in 1841.  At least two of Laestadius's own sons predeceased him as well . Around 1833 Laestadius suffered from an ailment which the doctors first thought was pneumonia. He recovered. In the 1840s, Laestadius suffered from severe typhoid fever and later tuberculosis.  Towards the end of his life, Laestadius experienced "impending blindness" and contracted a cholera-like illness.

How many years passed between his mothers death and the death of his brother Petrus?
17