21 squared

21² = 21 × 21 = 441

To square a number, multiply it by itself. 21 squared is written 21² or 21^2, and the answer is 441.

How to work out 21 squared

Direct: 21 × 21 = 441.
From the previous square: 20² = 400, and 21² = 400 + (2 × 21 − 1) = 400 + 41 = 441.
Split the number: 21 = 20 + 1, so 21² = 20² + 2 × 20 × 1 + 1² = 400 + 40 + 1 = 441.

Related

21 cubed = 9,261
The square root of 441 is 21, so 441 is a perfect square.

Squares near 21

Number	Squared
17	289
18	324
19	361
20	400
22	484
23	529
24	576
25	625

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