It could be 21.0/8

ref:https://old.reddit.com/r/tmobileisp/comments/1gg7361/why_is_...

I booted an LTE router using a T-Mobile SIM.

Within an hour I had changed WAN IP. Both were from AS749 US-DOD NIC

    in 33.79.135.0/24 & 21.140.100.0/24.