How to prove that an is equal difference function and equal ratio function
A (n + 1) - an = constant, it can be proved that an is an isochromatic function;
A (n + 1) / an = constant, it can be proved that an is a proportional function;
A (n + 1) - an = constant, it can be proved that an is an isochromatic function;
A (n + 1) / an = constant, it can be proved that an is a proportional function;