Question

show that 21n cannot end with 0,2,4,6 and8 for any natural number

Answer 1

prime factors of 21 are 3 and 7

we know that any number raised to any power can end with zero only if both 2 and 5 are it's factors

but for 21 neither 2 nor 5 are it's factors
hence it cannot end in zero whatever be the value of n