- Take a 2-digit number ending in 1.
- Subtract 1 from the number.
- Square the difference.
- Add the difference twice to its square.
- Add 1.

#### Example:

- If the number is
**41**, subtract 1: 41 - 1 = 40. - 40 × 40 = 1600 (square the difference).
- 1600 + 40 + 40 = 1680 (add the difference twice

to its square). - 1680 + 1 = 1681 (add 1).
- So
**41 × 41 = 1681**.

** See the pattern?**

- For 71 × 71, subtract 1: 71 - 1 = 70.
- 70 × 70 = 4900 (square the difference).
- 4900 + 70 + 70 = 5040 (add the difference twice

to its square). - 5040 + 1 = 5041 (add 1).
- So
**71 × 71 = 5041**.

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