123457

This number is a prime.

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The smallest prime whose 2nd, 3rd, 4th, and 5th digits are 2, 3, 4, and 5 respectively (OEIS A371845). Coincidentally, 6 is absent from the number. This is also the smallest 6-digit prime with strictly increasing digits (OEIS A071362). If its digits are taken as (a, b, c, d, e, f) = (1, 2, 3, 4, 5, 7), then except the initial term a!² = 1, all partial sums of squared factorials (a!² + b!², a!² + b!² + c!², …) are prime. [Ahmed]