None (83 words)
900, 901, 902, 903, 904, 905, 906, 908, 909, 910, 911, 912, 913, 914, 915, 916, 917, 918, 919, 920, 922, 924, 925, 926, 928, 929, 930, 931, 932, 933, 934, 935, 936, 937, 938, 940, 941, 942, 943, 944, 945, 946, 948, 949, 950, 951, 952, 953, 954, 955, 958, 959, 960, 961, 962, 963, 964, 965, 966, 967, 968, 970, 971, 973, 974, 976, 977, 978, 979, 980, 981, 983, 985, 986, 987, 988, 991, 992, 993, 994, 995, 997, 999
Once (18 words)
907, 921, 923, 927, 939, 947, 956, 957, 969, 972, 975, 982, 984, 989, 990, 996, 998, 1000