translate English to French: The series is obtained as follows:+3, ×2, +5, ×2 (i.e, 2 + 3; 5 × 2; 10 + 5; 15 × 2 ).
La série s'obtient comme suit : +3, ×2, +5, ×2 (soit, 2 + 3; 5 × 2; 10 + 5; 15 × 2 ).