I want to know, if is possible found the arithmetic progression of four square number, with the same common difference.
\begin{align} \ & a^2 +r = b^2 \\ & b^2 +r = c^2 \\ & c^2 +r = d^2 \\ \end{align}
where a,b,c,d,r $\in\mathbb{N}$
Hence, I found only triple succession.
For example: 1,5,7 because \begin{align} \ & 1^2 +24 = 5^2 \\ & 5^2 +24 = 7^2 \\ \end{align} where the ratio is 24.
but I can't found a example with four number and the same common difference. at worst. Could you demonstrate that nonexistent using reductio ad absurdum to this statement?.