Here's the countdown, skipping primes and 12:
100, 99, 98, 97 (prime), 96, 95 (prime), 94, 93 (prime), 92, 91 (prime), 90, 89 (prime), 88, 87 (prime), 86, 85 (prime), 84, 83 (prime), 82, 81, 80, 79 (prime), 78, 77 (prime), 76, 75, 74, 73 (prime), 72, 71 (prime), 70, 69 (prime), 68, 67 (prime), 66, 65 (prime), 64, 63, 62, 61 (prime), 60, 59 (prime), 58, 57, 56, 55 (prime), 54, 53 (prime), 52, 51, 50, 49 (prime), 48, 47 (prime), 46, 45, 44, 43 (prime), 42, 41 (prime), 40, 39 (prime), 38, 37 (prime), 36, 35 (prime), 34, 33 (prime), 32, 31 (prime), 30, 29 (prime), 28, 27, 26, 25 (prime), 24, 23 (prime), 22, 21, 20, 19 (prime), 18, 17 (prime), 16, 15, 14, 13 (prime), 11 (prime), 10, 9, 8, 7 (prime), 6, 5 (prime), 4, 3 (prime), 2, 1.