MathCastle
ChallengeSuperchallenge

Challenge · Superchallenge problem

A nonzero residue rr modulo 1919 is a QUADRATIC RESIDUE if r≡x2r \equiv x^2 for some xx. How many rr with 1≤r≤171 \le r \le 17 are such that BOTH rr and r+1r+1 are quadratic residues mod 1919?

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