D. R. Kaprekar
Indian mathematician D. R. Kaprekar is best remembered for his discovery of the Kaprekar constant in 1976. The constant is the number 6174.
Take any four-digit number in which not all digits are alike. Arrange the digits in descending order and then reverse them to make a new number. Subtract the new number from the first number. If this process is repeated with the difference, eventually in about eight steps, the constant 6174 is arrived at.
Example: 4527
7542 - 2457 = 5085
8550 - 0558 = 7992
9972 - 2799 = 7173
7731 - 1377 = 6354
6543 - 3456 = 3087
8730 - 0378 = 8352
8532 - 2358 = 6174
7641 - 1467 = 6174
