Mr Kaprekar and his numbers

I first came across the name of Mr Kaprekar in the mid-70s, when the door of a room in a remote corner of our hostel in IIT Kanpur had a chalked handwritten inscription of Mr D R Kaprekar. My classmates briefly mentioned that it was occupied by an elderly gentleman who was a guest of our Mathematics department.

A few decades later, I came across this article:

It is interesting that a mathematics teacher in a small town came up with various sets of numbers, long before computers or calculators existed. He lived in obscurity until Martin Gardner discovered his work and wrote about it in the “Scientific American” in 1975. Today his work is better known.

In particular, he is known for the Kaprekar constant 6174 (see explanation in above link)

Then there are the Kaprekar numbers.

The Devlali numbers or self numbers (as he was living in Devlali, near Nasik).

The Harshad numbers (based on a Sanskrit word, not Mehtaji).

The Demlo numbers.

Devlali also got itself into the English language because it was a rest camp for British soldiers before they returned home. Thus the phrase “Gone doolally” meant someone who had a mental problem.

As for Demlo, it appears to be a contraction of Dombivili (which meets the stipulation of being 30 miles from Bombay VT).