Unprimeable numbers | Rosetta Code | #16
URL to the problem page: http://rosettacode.org/wiki/Unprimeable_numbers As used here, all unprimeable numbers (positive integers) are always expressed in base ten. Unprimeable numbers are composite numbers that always remain composite when a single decimal digit of the number is changed. (arithmetic) that cannot be turned into a prime number by changing just one of its digits to any other digit. Unprimeable numbers are also spelled: unprimable. All one─ and two─digit numbers can be turned into primes by changing a single decimal digit. Examples: 190 isn't unprimeable, because by changing the zero digit into a three yields 193, which is a prime. The number 200 is unprimeable, since none of the numbers 201, 202, 203, ··· 209 are prime, and all the other numbers obtained by changing a single digit to produce 100, 300, 400, ··· 900, or 210, 220, 230, ··· 290 which are all even. It is valid to change 189 into 089 by changing the 1 (one) into a 0 (zero), which then th...
