Enter a positive integer.

Output will be shown here

Squared digit sum.

Let n be a positive integer. If you repeatedly replace n by the sum of the square of each digit, it will either end at 1 or cycle between the eight values 4, 16, 37, 58, 89, 145, 42, 20.

Source: https://johndcook.com/blog/2018/03/24/squared-digit-sum/

Related: Happy number