Alright, let's work through 21689399 times 64639402 step by step
21689399 × 64639402 = 64639402 × (21689399)
+ 64639402 × 9 that results in 581754618
+ 64639402 × 90 yielding 5817546180
+ 64639402 × 300 that is equal 19391820600
+ 64639402 × 9000 what gives us 581754618000
+ 64639402 × 80000 that is equal 5171152160000
+ 64639402 × 600000 what gives us 38783641200000
+ 64639402 × 1000000 resulting in 64639402000000
+ 64639402 × 20000000 which equals 1292788040000000

= 1401989781099398
