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Omni-MATH / Find the least positive integer N>1 satisfying the following two properties: There exists a positive integer a such that N=a(2a−1). The sum 1+2+⋯+(N−1) is divisible by k for every …

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problem

Find the least positive integer N>1N>1 satisfying the following two properties: There exists a positive integer aa such that N=a(2a−1)N=a(2 a-1). The sum 1+2+⋯+(N−1)1+2+\cdots+(N-1) is divisible by kk for every integer 1≤k≤101 \leq k \leq 10.
Plain-text mathematical notation (without MathML)
Find the least positive integer N>1 satisfying the following two properties: There exists a positive integer a such that N=a(2a−1). The sum 1+2+⋯+(N−1) is divisible by k for every integer 1≤k≤10.
Original LaTeX notation
Find the least positive integer $N>1$ satisfying the following two properties: There exists a positive integer $a$ such that $N=a(2 a-1)$. The sum $1+2+\cdots+(N-1)$ is divisible by $k$ for every integer $1 \leq k \leq 10$.

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