1365

This number is a composite.

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1365 is the product of the first 4 odd Mersenne prime exponents (3, 5, 7, 13), which are also the first 4 Fortunate primes. Interestingly, it also equals σ₂(2⁵), the sum of the squares of the divisors of 2⁵, which expands to the geometric series 4⁰ + 4¹ + 4² + 4³ + 4⁴ + 4⁵. [Ahmed]