Determine the number of non-negative integers x with x < 1010 that have a digit sum of 21.
No 2 digit numbers work, the largest sod would be 18.
No 4 digit numbers under 1010 work.
The possible 4 digit numbers under these constraints all start with 100 and so have a maximum sod of 10.
3 digit numbers include (# permutations):
399 (3)
489 (6)
579 (6)
588 (3)
669 (3)
678 (6)
777 (1)
-------
tot (28)
Thus there are exactly 28 such numbers.
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Posted by Larry
on 2024-12-13 10:20:18 |
Analytic solution