Problem Statement

Repunits are numbers that consist entirely of repetitions of the digit one (unity). The notation Rn symbolizes the repunit made up of n ones. Every prime p larger than 5, evenly divides the repunit Rp-1.

The repunit R6 is evenly divisible by 7. 111111 / 7 = 15873 The repunit R42 is evenly divisible by 43. 111111111111111111111111111111111111111111 / 43 = 2583979328165374677002583979328165374677 And so on.

There are composite numbers that also have this same property. They are often referred to as deceptive non-primes or deceptive numbers.

The repunit R90 is evenly divisible by the composite number 91 (=7*13).

Let's start with the solution:

val .isPrime = f .i == 2 or .i > 2 and not any f(.x) .i div .x, pseries 2 .. .i ^/ 2

var .nums = []
var .repunit = 111_111

for .n = 9; len(.nums) < 10; .n += 2 {
    .repunit = .repunit x 100 + 11
    if not .isPrime(.n) and .repunit div .n {
        .nums = more .nums, .n
    }
}

writeln .nums