Fourth Power is Sum of 2 Triangular Numbers

Theorem
Let $n \in \Z$ be an integer.

Then:
 * $\exists a, b \in \Z_{\ge 0}: n^4 = T_a + T_b$

where $T_a$ and $T_b$ are triangular numbers.

That is, the $4$th power of an integer equals the sum of two triangular numbers.