It is always a big question since 2009 but after many years, two past halvings in 2013 and 2017 as well as some past market cycles, we can see that halvings decrease block rewards for Bitcoin miners but in a correlation of Bitcoin price which increases after each halving.
Firstly you might have missed up some dates, I think you started counting bitcoin halving from 2009 with every four years interval which gave you the 2013, but the first bitcoin halving actually occurred In November 2012, where the block rewards was reduced 50btc per block to 25btc. Then the subsequent block reward halving occurred in 2016, and 2020 been the last time it occurred.