In the film, characters move from cell to cell, and each cell is labeled by three numbers, with each of these numbers being in the range 1-999. They learn to avoid those cells having a number which is a prime or a power of a prime.

There are 193 numbers below 1000 which are a prime or a power of a prime. This total is made up of the 168 primes less than 1000, namely

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997

plus the 11 numbers which are squares of primes

4 = 2^{2}, 9 = 3^{2}, 25 = 5^{2}, 49 = 7^{2}, 121 = 11^{2}, 169 = 13^{2}, 289 =
17^{2}, 361 = 19^{2}, 529 = 23^{2}, 841 = 29^{2}, 961 = 31^{2}

the 4 numbers which are cubes of primes

8 = 2^{3}, 27 = 3^{3}, 125 = 5^{3}, 343 = 7^{3}

the 3 numbers which are fourth powers of primes

16 = 2^{4}, 81 = 3^{4}, 625 = 5^{4}

and the following seven numbers which are higher powers of primes

32 = 2^{5}, 243 = 3^{5}, 64 = 2^{6}, 729 = 3^{6}, 128 = 2^{7}, 256 = 2^{8}, 512 = 2^{9}

So the probability that a single number less than 1000 chosen at
random is not a prime or a power of a prime is approximately
(999-193)/999 = 0.807, and the probability that three chosen at random
all have this property is approximately 0.807^{3} = 0.525, or slightly
better than 50:50.

Maintained by Chris Eilbeck/Heriot-Watt University, Edinburgh/ J.C.Eilbeck@hw.ac.uk