A good answer might be:

It activates Triangle() with a parameter of 2.

Yet Another Activation

Here is the new picture. You may be a bit uneasy about something called "Triangle" being active multiple times. But this is perfectly fine. Think of each activation as being a "clone" of Triangle that has been given its own little task.



What does the activation Triangle(2) do?

int Triangle( int N )
  if ( N == 1 )
    return 1;
    return N + Triangle( N-1 );