This is a thought process ........use with your workout to see if you can find the gap in the next number s 

If one number falls from the groups below we can expect another to fall from it ........ 

204, 207,208, 210, 211, 213, 215, 221, 222, 223, 224, 225, 226, 227,228,229,232, 234, 239,

242, 243, 245, 252, 253, 254, 255, 256, 258, 259, 260, 262, 265, 270, 287, 292, 295, 297,

gaps 33,44,55,

        30x 31x 32x 34x 35x 36x 37x 38x39x

        40x 41x 42x 44x 45x 46x 47x 48x49x

        50x 51x 52x 54x 55x 56x 57x 58x59x

600, 607, 615, 619, 623, 625, 627, 635, 638, 643, 644, 645, 647,646, 648, 656, 657, 660,

661, 662, 666, 668, 669, 670, 673, 675, 680, 682, 686, 691, 692, 695,

      gap 77x 

      70x,71x,72x,73x,74x,75x,76x,77x,78x,79x

800, 803, 808, 809, 814, 815, 816, 817, 818, 819, 821, 823, 825, 826, 828, 831, 832,

833, 834, 835, 836, 838, 841, 843, 849, 851, 852, 855, 856, 859, 862, 869, 870, 874, 881, 884, 885, 886, 887, 892, 896

gap 99x