Sunday, May 16, 2010

Numerical Palindromes

Someone at work put up the following pattern on a whiteboard

1 x 1 = 1
11 x 11 = 121
111 x 111 = 12321
1111 x 1111 = 1234321
11111 x 11111 = 123454321
111111 x 111111 = 12345654321
1111111 x 1111111 = 1234567654321
11111111 x 11111111 = 123456787654321
111111111 x 111111111 = 12345678987654321

So squaring a number that is all 1’s gives a numerical palindrome. Why?

Well there is a nice simple visual answer
image
More on such patterns here.