Alright, let's work through 20821870 times 21240659 step by step
20821870 × 21240659 = 21240659 × (20821870)
+ 21240659 × 0 that equals 0
+ 21240659 × 70 producing 1486846130
+ 21240659 × 800 producing 16992527200
+ 21240659 × 1000 which equals 21240659000
+ 21240659 × 20000 producing 424813180000
+ 21240659 × 800000 that is equal 16992527200000
+ 21240659 × 0000000 producing 0
+ 21240659 × 20000000 that equals 424813180000000

= 442270240412330
