Every answer takes you to the table. Pick a question:
Every perfect square ends in one of these six digits. Numbers ending in 2, 3, 7, or 8 are never perfect squares.
Click a card to highlight every matching square in the table above.
Squares that read the same forwards and backwards.
Every square of a number ending in 5 ends in 25.
Squares whose root appears in an integer right triangle.
Squares of prime numbers — their only divisors are 1, p, and p².
Both a perfect square and a triangular number (1+2+...+n).
Facts true of every perfect square — useful for spotting them and ruling them out.
n² equals the sum of the first n odd numbers. So 1+3+5+7+9 = 25 = 5².
Perfect squares are the only positive integers with an odd count of divisors. 36 has 9 divisors: 1, 2, 3, 4, 6, 9, 12, 18, 36.
The difference between n² and (n+1)² is always 2n+1 — the next odd number.
10²=100, 11²=121, gap=21Every perfect square is 0 or 1 mod 4 — never 2 or 3. Combined with the last-digit rule, this rejects most non-squares instantly.
1543 mod 4 = 3 → not a square