Alright, let's work through 81321121 times 15108235 step by step
81321121 × 15108235 = 15108235 × (81321121)
+ 15108235 × 1 giving us 15108235
+ 15108235 × 20 producing 302164700
+ 15108235 × 100 which equals 1510823500
+ 15108235 × 1000 resulting in 15108235000
+ 15108235 × 20000 resulting in 302164700000
+ 15108235 × 300000 that results in 4532470500000
+ 15108235 × 1000000 that is equal 15108235000000
+ 15108235 × 80000000 producing 1208658800000000

= 1228618606531435
