Concept:The series is made of alternating pairs, where the second number follows a cube pattern.Explanation:Write the series as pairs: (3,8),(5,27),(8,64),(12,125),(17,?).The first numbers are 3,5,8,12,17, increasing by +2,+3,+4,+5.The second numbers are 8,27,64,125, which are cubes: 23,33,43,53.The next cube is 63=216.So the missing number is 216.
