Just another counting problem

An integer is called a 20 20 -number if the sum of its digits is equal to 20. 20. How many even 20 20 -numbers are there less than or equal to 100 , 000 \numcomma{100000} ?

For example, 758 , 758, 19 , 730 , \numcomma{19730}, and 44 , 552 \numcomma{44552} are 20 20 -numbers because

7 + 5 + 8 = 20 , 1 + 9 + 3 + 7 + 0 = 20 , and 4 + 4 + 5 + 5 + 2 = 20. 7+5+8=20, 1+9+3+7+0=20, \text{ and } 4+4+5+5+2=20 .


The answer is 2891.

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