Solution:
We immediately exclude the case in which n has all digits different from zero, since in this case we have n0=n. There remain therefore two possibilities:
1) n has the third digit equal to zero; the decimal representation of n is of the type n=ab0, n0=ab and n0∣n for every choice of a∈{1,…,9} and of b∈{0,1,…,9}. Regarding this case, there are thus 9×10=90 possibilities for n.
2) n has the third digit different from zero but the second equal to zero; in this case n is written in the form a0b and n0 in the form ab. Recalling the meaning of decimal notation, we thus look for the cases in which 10a+b divides 100a+b. Since certainly 10a+b divides 10(10a+b)=100a+10b, it is also equivalent to see when 10a+b divides the difference (100a+10b)−(10a+b)=9b.
Writing k(10a+b)=100a+b and considering the last decimal digit, we obtain that (k−1)b is divisible by 10, so that at least one of k−1 and b is divisible by 5. Since evidently 1<k<10 and 1≤b≤9, we have that k−1=5 or b=5.
For k−1=5 we obtain 60a+6b=100a+b, from which b=8a and hence a=1, b=8. One checks that n=108 is indeed a solution, since 18 divides 108.
For b=5 we use the equivalent property that 10a+b divides 9b, which becomes 10a+5 divides 45; one sees immediately that the divisors of 45 of the form 10a+5 with a≥1 are 15 and 45, giving the two solutions n=105 (15 divides 105) and n=405 (45 divides 405).
In conclusion, there are 90 solutions in case 1) and 3 solutions in case 2), for a total of 93 solutions.