What is the name of the algorithm for multiplying two digit numbers by 11 in you head by adding the two digits to make the middle result digit?

Question

My father(70, I’m 40) said:

You can multiply two digit numbers by 11 in your head by adding your two digits and inserting it in the middle of your original two digits. So 13 x 11 => 1 + 3 = 4 => 143

This process must have a name in the mathematical world.

My question is: What is the name of the algorithm for multiplying two digit numbers by 11 in you head by adding the two digits to make the middle result digit?

Answer 1

The multiplication algorithm is a convolution of the digits - at least as long as no overflow (carry) occurs.