User:David Cobac

Maths teacher (secondary school) in France. Twitter account: @david_cobac

- Smallest nonprime number <= 10^n (n>=1) with maximum distance from a prime. A306475

- a(n) = (n-1)! * (10^n - 1) / 9. A323416

- a(n) = n if n is 1 or prime; otherwise (1) let m = (concatenation of the two divisors in the middle of rows of A027750(n)), (2) if m is prime then a(n) = m, otherwise return to (1) with n=m. A329181