\[ (n+1) a^{2 n} y(x)^{2 n+1}+y''(x)-y(x)=0 \] ✓ Mathematica : cpu = 0.148189 (sec), leaf count = 47
\[\text {Solve}\left [\int _1^{y(x)}\frac {1}{\sqrt {c_1-K[1]^2 \left (a^{2 n} K[1]^{2 n}-1\right )}}dK[1]{}^2=(x+c_2){}^2,y(x)\right ]\] ✓ Maple : cpu = 0.243 (sec), leaf count = 73
\[\left \{-c_{2}-x +\int _{}^{y \left (x \right )}\frac {1}{\sqrt {\textit {\_a}^{2}-\textit {\_a}^{2 n +2} a^{2 n}+c_{1}}}d \textit {\_a} = 0, -c_{2}-x +\int _{}^{y \left (x \right )}-\frac {1}{\sqrt {\textit {\_a}^{2}-\textit {\_a}^{2 n +2} a^{2 n}+c_{1}}}d \textit {\_a} = 0\right \}\]