Question 344524
let a,a+1 the integers in question : a(a+1)=9*(a+a+1)-9
 
a^2+a=18a+9-9
a^2=17a
 
a=0 : verif : 0*1=0, 9*(0+1)-9=9-9=0.
 
a=17 : verif : 17*18=180+70+56=306, 9*(17+18)-9=9*35-9=9*34=340-34=306.