Consider each position in the letter cluster separately.
Series:
HLPT, HOUA, HRZH, HUEO, ?
1st letter
H, H, H, H → constant
Next = H
2nd letter
L, O, R, U
Positions: 12, 15, 18, 21
Pattern: +3
Next: 21 + 3 = 24 → X
3rd letter
P, U, Z, E
Positions: 16, 21, 26, 5
Pattern: +5 (wrapping after Z)
Next: 5 + 5 = 10 → J
4th letter
T, A, H, O
Positions: 20, 1, 8, 15
Pattern: +7 (wrapping after Z)
Next: 15 + 7 = 22 → V
Final Answer:
HXJV