Do you know......

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.)


And...


Letter 'c' does not appear anywhere in in the spellings of entire
English Counting...!!