ABCD

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 the spellings of entire English Counting. Just try .....

Information on the great effort Mhkour

thx 4 that info
god bless u

You are welcome