16, ?, 21, 30, 46, 71, 107

The given series is in the below pattern,
First term = 16
Second term = First term + 1²
⇒ Second term = 16 + 1² = 17
∴ ? = 17
Third term = Second term + 2²
⇒ Third term = 17 + 2² = 21
Fourth term = Third term + 3²
⇒ Fourth term = 21 + 3² = 30 ;
Fifth term = Fourth term + 4²
⇒ Fifth term = 30 + 4² = 46 ;
Similarly , we can find all others terms also.
Sixth term = Fifth term + 5²
⇒ Sixth term = 46 + 5² = 71;
Seventh term = Sixth term + 6²
⇒ Sixth term = 71 + 6² = 107
Hence , Second term = 17