Find all positive integers $a$ for which there exists some positive integer $b$ s.t. $(2^a-1)\mid(b^2+9)$
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Find all positive integers $a$ for which there exists some positive integer $b$ s.t.
$(2^a-1)\mid(b^2+9)$
elementary-number-theory
asked 2012-11-12
user id:49099
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Welcome to SE. It would be helpful if you explain what you tried so far and where you got stuck. This will help you get better answers to your question. – 2012-11-12
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This is an old question from an IMO Shortlist (1998?). – 2013-09-03