A simple mathematical operation in each number of the sequence 14, 18, 20, 24, 30, 32, ... results in a sequence with respect to prime numbers. Which one of the following is the next number in the sequence?
Answer & explanation
Answer: (c) 38
Subtracting 1 from each term gives 13, 17, 19, 23, 29, 31 — consecutive prime numbers. The next prime is 37, so the next term is 37 + 1 = 38.
- Subtract 1: 14 → 13, 18 → 17, 20 → 19, 24 → 23, 30 → 29, 32 → 31.
- 13, 17, 19, 23, 29, 31 are consecutive primes.
- The next prime after 31 is 37 (33, 35 are composite).
- Next term = 37 + 1 = 38.
Remember · When a series 'relates to primes', try adding or subtracting 1 or 2 to each term and look for consecutive primes.
Question and answer: UPSC's official GS Paper II (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·