On an assertion of Ramanujan concerning binary quadratic forms (Q2277002)

In Ramanujan's notebook there is the following statement: ``If a prime of the form \(An+B\) can be expressed as \(ax^ 2-by^ 2,\) then a prime of the form \(An-B\) can be expressed as \(bx^ 2-ay^ 2\)''. A precise form of this assertion is proved by means of the classical theory of binary quadratic forms and several examples are given.