every different place i check says https://blockchain.info/address/1MtR9nBGfWBLY23q4dRGRjjzBBiEdxRmC3 is a valid bitcoin address and i've tried a few different places. End of the day i don't really care, it's an empty address, but everywhere i check says it's valid.
The ADDRESS is valid but no wallet should have imported the PRIVATE KEY because it is invalid.