Which of these numbers is NEITHER a triangular number NOR a Virahānka number? (Triangular: 1,3,6,10,15,21,... Virahānka: 1,2,3,5,8,13,21,...)
- A.10
- B.13
- C.16 ✓
- D.21
Explanation: 10 is triangular, 13 is a Virahānka number, and 21 is both — but 16 appears in neither list.
Class 6 IMO Mathematics Olympiad practice · Algebraic Thinking · Patterns in Mathematics
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