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2009 xIMC keystage2-EMIC individual Question 14

xIMC · 2009 xIMC keystage2-EMIC individual

Question 14

Four positive integers $a\lt b\lt c\lt d$ form a friendly group if $(d-c)(c-b)(b-a)$ is divisible by $2009$. How many friendly groups lie in $1$ through $60$?