What is X in the sequence 1, 3, 6, 11, 18, X, 42?

उत्तर देखें और व्याख्या

उत्तर: (C) 29

व्याख्या

Differences are primes 2, 3, 5, 7, 11, 13: 18 + 11 = 29, 29 + 13 = 42. (Answer as per the official UPSC answer key.)