ABCD

A, B, C and D are all very uncommon in English spellings of numbers

• The letter 'A' is not used until Thousand (1,000)

• The letter 'B' does not show up until Billion (1,000,000,000)

• The letter 'C' is not used until Octillion (27th power of 10)

• The letter 'D' does not appear until Hundred (100)