Four letter-clusters have been given, out of which three are alike in some manner and one is different. Select the letter-cluster that is different.

IPVA

THE LOGIC;

1) HNTZ,

H → (+6) → N → (+6) → T → (+6) → Z

2) AGMS,

A → (+6) → G → (+6) → M → (+6) → S

3) IPVA,

I → (+7) → P → (+6) → V → (+5) → A

4) VBHN,

V → (+6) → B → (+6) → H → (+6) → N

Thus, IPVA is the odd one.