Q. Find the odd number in the series: 
1, 2, 8, 21, 88, 445

Explanation by: Santosh Mishra

As per the details in the question the series is in the form of
First term = 1
Second term = ( First term × Variable ) + Variable
⇒ Second term = ( 1 × 1 ) + 1 = 2
Third term = ( First term × Variable ) + Variable
⇒ Third term = ( 2 × 2 ) + 2 = 8 , So 8 is wrong. we get 6 as Third term.
Similarly , we can find the all terms also.
Fourth term = ( 6 × 3 ) + 3 = 21
Fifth term = ( 21 × 4 ) + 4 = 88
Sixth term = ( 88 × 5 ) + 5 = 445