The given series: Z1, Y4, X9, ______ The first element of each term is a letter that is in the reverse alphabetical order.
Z
−1
────▶
Y
−1
────▶
X
−1
────▶
W
Thus, the next term will start with 'W'. The second element of each term is a number which is a square of natural numbers starting from 1. 12=1;22=4;32=9;42=16 Hence, the next term will be W16.