$$2^{3 n}-7 n-1 \text { is divisible by }$$

The total number of terms in the expansion of $$(x+y)^{60}+(x-y)^{60}$$ is

The coefficient of $$x^{29}$$ in the expansion of $$\left(1-3 x+3 x^2-x^3\right)^{15}$$ is

In the expansion of $$\left(1+3 x+3 x^2+x^3\right)^{2 n}$$, the term which has greatest binomial coefficient, is