This sequence lists prime numbers in ascending order - numbers divisible only by 1 and themselves. Starting with 2 (the only even prime), the series continues 3, 5, 7, 11, 13, 17, 19, and the next prime is 23. Options A (21 = 3x7), B (22 = 2x11), and D (24 = 2x12) are all composite numbers.