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deficient n.  and  triangular n.

First numbers that belong to both sets:

1, 3, 10, 15, 21, 45, 55, 91, 105, 136, 153, 171, 190, 231, 253, 325, 351, 406, 435, 465, 561, 595, 703, 741, 861, 903, 946, 1035, 1081, 1225, 1275, 1378, 1431, 1485, 1653, 1711, 1891, 1953, 2145, 2211, 2278, 2415, 2485, 2701, 2775, 2926, 3003, 3081, 3321, 3403, 3655, 3741, 3916, 4005, 4186, 4371, 4465, 4753, 4851, 5050, 5151, 5253, 5356, 5565, 5671, 5995, 6105, 6441, 6555, 6670, 6903, 7021, 7381, 7503, 7750, 8001, 8385, 8515, 8911, 9045, 9316, 9453, 9591, 10011, 10153, 10585, 10731, 11026, 11175, 11325, 11476, 11781, 11935, 12403, 12561, 13041, 13203, 13366, 13695, 13861, 14365, 14535, 14878, 15051, 15225, 15753, 15931, 16471, 16653, 17205, 17391, 17578, 18145, 18721, 18915, 19306, 19503, 19701, 20301, 20503, 21115, 21321, 22155, 22366, 22791, 23005, 23653, 23871, 24531, 24753, 25425, 25651, 26335, 27028, 27261, 27495, 27730, 28203, 28441, 29161, 29403, 30135, 30381, 31125, 31375, 32131, 32385, 32896, 33153, 33411, 34191, 34453, 35245, 35511, 36046, 36315, 36585, 36856, 37401, 37675, 38503, 38781, 39621, 39903, 40186, 40755, 41041, 41905, 42195, 42778, 43071, 43365, 44253, 44551, 45451, 45753, 46665, 46971, 47278, 47895, 48205, 49141, 49455, 50086, 50403, 50721, 51681, 52003, 52975, 53301, 54615, 54946, 55611, 55945, 56953, 57291, 58311, 58653, 59685, 60031, 61075, 62481, 62835, 63190, 63903, 64261, 65341, 65703, 66795, 67161, 67528, 68265, 68635, 69751, 70125, 70876, 71253, 71631, 72010, 72771, 73153, 74305, 74691, 75466, 75855, 76245, 77421, 77815, 79003, 79401, 80601, 81003, 81406, 82621, 83845, 84255, 85078, 85491, 85905, 87153, 87571, 88831, 89253, 90525, 90951, 91378, 92235, 92665, 93961, 94395, 95266, 95703, 96141, 97461, 97903, 99235, 99681, 101025, 101926, 102831, 103285, 104653, 105111, 106030, 106491, 106953, 107416, 108345, 108811, 110215, 110685, 111628, 112101, 112575, 114003, 114481, 115921, 116403, 117370, 117855.

Some larger examples :