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Number Theory
Units digit of powers
Find the last digit of a^n using its cycle.
Practise →Modular exponentiation
Compute a^n mod m without a calculator.
Practise →Counting divisors
How many divisors does a number have?
Practise →GCD & LCM
Least common multiples from prime structure.
Practise →Chinese Remainder
Smallest number with given remainders.
Practise →Trailing zeros of n!
Count zeros at the end of a factorial.
Practise →