Răspuns :
1 2 3 6( 2 3 4 ) 9 (3 4 5 )12 (4 5 6) 15 (5 6 7) 18 (6 7 8) 21 (7 8 9) 24..........
1 2 3 6 ( 2 3 4 ) 9 (3 4 5 ) 12 ( 4 5 6) 15 ( 5 6 7 ) 18 (6 7 8 ) 21 ( 7 8 9) ........