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tau n.  and  unprimeable n.

First numbers that belong to both sets:

204, 328, 516, 536, 625, 896, 1260, 1332, 1336, 1344, 1356, 1644, 1680, 1688, 1920, 1928, 2076, 2104, 2196, 2320, 2364, 2480, 2488, 2560, 2824, 2944, 2984, 2988, 3096, 3156, 3176, 3240, 3280, 3420, 3684, 3688, 3744, 3756, 3816, 3896, 3972, 3992, 4032, 4068, 4080, 4140, 4164, 4168, 4184, 4188, 4308, 4476, 4552, 4572, 4616, 4716, 4744, 4764, 4824, 4856, 4896, 4928, 5040, 5048, 5128, 5248, 5256, 5316, 5360, 5364, 5464, 5604, 5608, 5672, 5752, 5760, 5912, 5944, 5976, 6184, 6408, 6432, 6516, 6624, 6640, 6720, 6756, 6816, 6924, 6936, 7092, 7096, 7116, 7164, 7272, 7380, 7404, 7428, 7440, 7616, 7736, 7760, 7764, 7768, 7776, 7808, 7836, 7976, 8028, 8072, 8076, 8136, 8152, 8392, 8400, 8408, 8488, 8552, 8720, 8724, 8728, 8796, 8872, 8916, 8984, 9032, 9036, 9084, 9088, 9144, 9304, 9360, 9368, 9444, 9448, 9504, 9564, 9704, 9708, 9756, 9840, 9848, 9864, 9896, 9992, 10080, 10232, 10236, 10376, 10408, 10548, 10572, 10640, 10644, 10764, 10800, 10872, 10960, 11120, 11304, 11340, 11604, 11608, 11648, 11724, 11760, 11768, 11796, 11844, 11848, 11912, 11916, 11992, 12024, 12060, 12080, 12088, 12132, 12184, 12384, 12468, 12664, 12776, 12872, 12992, 13016, 13116, 13200, 13236, 13344, 13352, 13356, 13404, 13544, 13548, 13812, 13864, 13896, 13952, 13956, 13976, 14160, 14184, 14216, 14264, 14312, 14316, 14496, 14584, 14604, 14640, 14648, 14676, 14976, 15000, 15112, 15156, 15208, 15592, 15636, 15832, 15840, 15896, 15944, 15948, 16020, 16024, 16164, 16200, 16404, 16504, 16596, 16712, 16776, 16792, 17144, 17148, 17224, 17244, 17268, 17280, 17288, 17360, 17364, 17520, 17640, 17676, 17772, 17840, 17844, 17944, 17964, 18000, 18008, 18108, 18152, 18248, 18276, 18296, 18336, 18472, 18560, 18640, 18720, 18728, 18816, 18828, 18936, 18960, 18968, 18996, 19048, 19104, 19112, 19192, 19296, 19328, 19356, 19368, 19496.

Some larger examples :