If for positive integers r > 1, n > 2, the coefficients of the (3r) th and (r + 2)th powers of x in the expansion of (1 + x) 2n are equal, then n is equal to :

If for positive integers $r>1, n>2$, the coefficients of the $(3 r)^{\text {th }}$ and $(r+2)^{\text {th }}$ powers of $x$ in the expansion of $(1+x)^{2 \mathrm{n}}$ are equal, then $n$ is equal to: $