A good
mnemonic for four, if you know some
Japanese, is to remember that "shi" means four in Japanese, and the Tengwar digit four looks like
hiragana "shi". (Is this a coincidence?)
More Tengwar digits, if I can remember:
Zero: Eleven:
@
@
@ @
@@@@ @ @
@ @ @ @
@ @@@@
@ @
@ @ @ @
@@@@ @@@@
Tengwar had two number systems, decimal and duodecimal. Which base was in use was indicated by means of special markings which I cannot remember.