\[(\ell+1)rf\left(\epsilon,\ell-1;r\right)-(2\ell+1)\left(\ell(\ell+1)-r\right)f%
\left(\epsilon,\ell;r\right)+\ell\left(1+(\ell+1)^{2}\epsilon\right)rf\left(%
\epsilon,\ell+1;r\right)=0,\]