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 .
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
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