Roble number III
A roble number is a positive integer that does not contain any of the digits 1, 4, and 3. The first few roble numbers are 2, 5, 6, 7, 8, 9, 20, 22, 25.... Find the sum of the first 143 roble numbers .
Related Problems: You might also want to try Roble Problem I and Roble Problem II .
The answer is 41053.
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1 solution
The first 143 roble numbers are 2 , 5 , 6 , . . . , 9 7 , 9 8 , 9 9 , 2 0 2 , 2 0 5 , 2 0 6 , . . . , 2 9 7 , 2 9 8 , 2 9 9 , 5 0 2 , 5 0 5 , 5 0 6 , . . . 5 9 7 , 5 9 8 , 5 9 9 excluding 5 9 7 , 5 9 8 , 5 9 9 ,so I'll subtract that at last.
The sum of the unit digit is 2 1 ( 2 + 5 + 6 + 7 + 8 + 9 ) = 7 7 7 ,
and the sum of the second digit is also 2 1 ( 2 + 5 + 6 + 7 + 8 + 9 ) = 7 7 7 ,
and the sum of the first digit is 4 9 ( 2 + 5 ) = 3 4 3 ,
so the sum is 3 4 3 0 0 + 7 7 7 0 + 7 7 7 = 4 2 8 4 7 ,
subtract the three number and get 4 1 0 5 3