Numerele de forma a7b sunt : - 171,172,173,174,175,176,177,178,179,271,272,273,274,275,276,277,278,279,371,372,373,374,375,376,377,378,379,471,472,473,474,475,476,477,478,479,571,572,573,574,575,576,577,578,579,671,672,673,674,675,676,677,678,679,771,772,773,774,775,776,777,778,779,871,872,873,874,875,876,877,878,879,971,972,973,974,975,976,977,978,979 in total sunt : 90 dacă-nu le-am numărat pe totate mai numarele pe toate încă odată
