Patterns in Numbers and Digits
Overview
Important
Patterns in numbers and digits often involve sequences, periodicity, and modular arithmetic. Recognizing these patterns allows us to predict future terms or properties of numbers, such as the last digit, the sum of digits, or the remainder when divided by a number.
Important properties
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Periodicity: Some patterns repeat after a fixed number of steps (period).
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Arithmetic and geometric sequences: Patterns can be based on adding or multiplying by a constant.
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Modular arithmetic: Patterns in digits, such as last digits or remainders, can be analyzed using congruences.
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Digit patterns: The behavior of digits (like the sum or last digit) often follows a cycle.
Practice
A. Decimal expansions and repeating fractions Verify these decimal expansions:
Prove that any cyclic permutation of its digits is also divisible by
Show that any purely periodic proper fraction equals a fraction whose numerator
is divisible by 7, prove that it is also divisible by 11, 13, and 15,873. In the
D. Base‑16 (hexadecimal) curiosities Does there exist a hexadecimal number that,
If this digit is moved to the front, the number doubles. Find the smallest such
Example: knowing that 93,767 is divisible by 41, conclude that 37,679 is divisib
Finding the Last Digit of a Large Multiplication
Finding the Last Digit of a Large Number
Finding the Last Two Digits of 22000
More practice problems →