Still, I bet you didn’t know this…
Letters ‘a’, ‘b’, ‘c’ &’d’ do not appear anywhere in the spellings of 1 To 99
Letter ’d’ comes for the first time in Hundred
Letters ‘a’, ‘b’ & ‘c’ do not appear anywhere in the spellings of 1 to 999
Letter ‘a’ comes for the first time in thousand
Letters ‘b’ & ‘c’ do not appear anywhere in the spellings of 1 to 999,999,999
Letter ‘b’ comes for the first time in Billion
&
Letter ‘c’ does not appear anywhere in the spellings of entire English Counting