jmc

Denote our number as $10a+b,$ where $a$ and $b$ represent the tens and units digit, respectively. It follows that $2ab=10a+b,$ or $$2a(b-5)-(b-5)=5$$ $$(2a-1)(b-5)=5.$$ We start by minimizing $a.$ If $2a-1=1$ and $b-5=5,$ $(a,b)=(1,10),$ which does not work because $b$ cannot exceed 9. Trying the second case, $2a-1=5$ and $b-5=1,$ leaving us with $(a,b)=(3,6).$ Thus, the smallest positive integer meeting the problem conditions is $\boxed{36}.$