The Guardian has a write-up on Russian political prisoners. Not all of them: the human rights group Memorial puts their total number at 77 while another recent estimate is 230, and the total number of people persecuted for political reasons since 2014 is probably in the thousands or even in the five digits.
Note that some have been charged or convicted of non-political crimes, on fabricated evidence, while others have been prosecuted as “extremists” under Russia’s notorious laws criminalizing “extremist” speech and assemblies. These laws, passed in 2002 and amended more than once (known as Article 282), enable the government – among other things – to block a person’s bank accounts on a mere suspicion of “extremist” speech. Curiously, some of Russia’s anti-Putinists want Article 282 to stay on the books, to be used against “genuine” extremists such as neo-Nazis. Some people never learn.