If S(x)=(1+x)+2(1+x)^2+3(1+x)^3+⋯+60(1+x)^60, x ≠ 0, and (60)^2 S(60)= a ( b )^b + b, where a, b ∈ N, then ( a + b ) equal to ____.

If $\displaystyle S(x)=(1+x)+2(1+x)^2+3(1+x)^3+\cdots+60(1+x)^{60}, x \neq 0$, and $\displaystyle (60)^2 S(60)=\mathrm{a}(\mathrm{b})^{\mathrm{b}}+\mathrm{b}$, where $\displaystyle \mathrm{a}, \mathrm{b} \in \mathrm{N}$, then $\displaystyle (\mathrm{a}+\mathrm{b})$ equal to $\displaystyle \_\_\_\_$.