400以内的合数有：

4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100, 102, 104, 105, 106, 108, 110, 111, 112, 114, 115, 116, 117, 118, 120, 121, 122, 124, 125, 126, 127, 128, 130, 132, 133, 134, 135, 136, 138, 139, 140, 141, 142, 144, 145, 146, 148, 149, 150, 151, 152, 154, 155, 156, 157, 158, 160, 161, 162, 164, 165, 166, 168, 169, 170, 171, 172, 174, 175, 176, 177, 178, 180, 181, 182, 184, 185, 186, 187, 188, 190, 191, 192, 194, 195, 196, 198, 199, 200, 201, 202, 204, 205, 206, 208, 209, 210, 211, 212, 214, 215, 216, 217, 218, 220, 221, 222, 224, 225, 226, 227, 228, 230, 231, 232, 234, 235, 236, 238, 239, 240, 241, 242, 244, 245, 246, 248, 249, 250, 251, 252, 254, 255, 256, 257, 258, 260, 261, 262, 264, 265, 266, 268, 269, 270, 271, 272, 274, 275, 276, 278, 279, 280, 281, 282,