2-in-1: Strange Number 6174 and College Humor for John Ellis

6174 is known as Kaprekar's constant^[1][2][3] after the Indian mathematician D. R. Kaprekar. This number is notable for the following property:

1. Take any four-digit number, using at least two different digits. (Leading zeros are allowed.)
2. Arrange the digits in ascending and then in descending order to get two four-digit numbers, adding leading zeros if necessary.
3. Subtract the smaller number from the bigger number.
4. Go back to step 2.

The above process, known as Kaprekar's routine, will always reach 6174 in at most 7 iterations.^[4] Once 6174 is reached, the process will continue yielding 7641 – 1467 = 6174. For example, choose 3524:

5432 – 2345 = 3087

8730 – 0378 = 8352

8532 – 2358 = 6174

The only four-digit numbers for which Kaprekar's routine does not reach 6174 are repdigits such as 1111, which give the result 0 after a single iteration. All other four-digit numbers eventually reach 6174 if leading zeros are used to keep the number of digits at 4:

2111 – 1112 = 0999

9990 – 0999 = 8991 (rather than 999 – 999 = 0)

9981 – 1899 = 8082

8820 – 0288 = 8532

8532 – 2358 = 6174

9831 reaches 6174 after 7 iterations:

9831 – 1389 = 8442

8442 – 2448 = 5994

9954 – 4599 = 5355

5553 – 3555 = 1998

9981 – 1899 = 8082

8820 – 0288 = 8532 (rather than 882 – 288 = 594)

8532 – 2358 = 6174

Note that in each iteration of Kaprekar's routine, the two numbers being subtracted one from the other have the same digit sum and hence the same remainder modulo 9. Therefore the result of each iteration of Kaprekar's routine is a multiple of 9.
495 is the equivalent constant for three-digit numbers. For five-digit numbers and above, there is no single equivalent constant; for each digit length the routine may terminate at one of several fixed values or may enter one of several loops instead.^[4]

See also

• Collatz conjecture

References

1. ^ Mysterious number 6174
2. ^ Kaprekar DR (1955). "An Interesting Property of the Number 6174". Scripta Mathematica 15: 244–245. 
3. ^ Kaprekar DR (1980). "On Kaprekar Numbers". Journal of Recreational Mathematics 13 (2): 81–82. 
4. ^ ^{a b} Weisstein, Eric W., "Kaprekar Routine" from MathWorld.

External links

• Mysterious Number 6174 Article
• The mysterious 6174 revisited
• Kaprekar Series Generator
• Online Kaprekar script

Retrieved from "http://en.wikipedia.org/wiki/6174_(number)"

Categories: Integers | Mathematical constants

See more funny videos and funny pictures at CollegeHumor.

Hey, I don't do this stuff! One of my college-aged kids showed it to me. It's from a site called www.collegehumor.com

But I think I know somebody who would like it .....

From the book "Not Even Wrong" (to which I give my highest recommendation) by Peter Woit:

The story behind this seems to be that particle theorist John Ellis and experimentalist Melissa Franklin were playing darts one evening at CERN in 1977, and a bet was made that would require Ellis to insert the word "penguin" somehow into his next research paper if he lost. He did lose, and was having a lot of trouble working out how he would do this. Finally, 'the answer came to him when one evening, leaving CERN, he dropped by to visit some friends where he smoked an 'illegal substance'. While working on his paper later that night 'in a moment of revelation he saw that the diagrams looked like penguins'.

Oo-o-h, looks, I see two penquins!
Luvz,
Heidi
Here's a video of me: