Alright, let's work through 21279831 times 81087264 step by step
21279831 × 81087264 = 81087264 × (21279831)
+ 81087264 × 1 that equals 81087264
+ 81087264 × 30 which equals 2432617920
+ 81087264 × 800 yielding 64869811200
+ 81087264 × 9000 yielding 729785376000
+ 81087264 × 70000 giving us 5676108480000
+ 81087264 × 200000 resulting in 16217452800000
+ 81087264 × 1000000 resulting in 81087264000000
+ 81087264 × 20000000 yielding 1621745280000000

= 1725523274172384
