Letters 'a', 'b', 'c' and 'd' do not appear if you spell any of the numbers between 1 and 99 [Funnily enough, letter 'd' comes for the first time in Hundred]
In addition, letters 'a', 'b' and 'c' do not appear anywhere in the spellings of
1 to 999 [Strange, but true, letter 'a' comes for the first time in Thousand]
Neither letter 'b' nor 'c' 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.