A function f(N) is defined as:
f(1)=sod(1²), f(2) = sod(12²)
f(3) = sod(121²), f(4) = sod(1212²), .... and, so on

Derive the general formula for f(N) in terms of N.

*** sod(x) denotes the sum of the digits of base ten expansion of x.

When you refer to the sum of the digits, is it only one iteration, or is it repeated until the sum is a single digit (I believe this is called the digital root)?

For example, 121² = 14,641.  Is sod(121²) = 16, or is it 7?

Posted by tomarken on 2014-03-03 16:25:03