Finding the first counter example to primes

FindPrimes.hs

module FindPrimes where

import Data.List ((\\))

setDifference = (\\)

primes = [ 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, 1009, 1013
         , 1019, 1021, 1031, 1033, 1039, 1049, 1051, 1061, 1063, 1069
         , 1087, 1091, 1093, 1097, 1103, 1109, 1117, 1123, 1129, 1151
         , 1153, 1163, 1171, 1181, 1187, 1193, 1201, 1213, 1217, 1223
         ]

possiblePrimes = filter isPrime [1..1223]
falsePositives = possiblePrimes `setDifference` primes

isPrime n
  | n < 2 = False
  | n == 2 = True
  | n == 3 = True
  | n > 3 =
    case (n `mod` 2, n `mod` 3) of
      (0, _) -> False
      (_, 0) -> False
      (1, _) -> True
      (_, 1) -> True
      otherwise -> False