NL-NWO 1989 Problem 1

For a sequence of integers $a_1,a_2,a_3,...$ with $0<a_1<a_2<a_3<...$ applies: $$a_n=4a_{n-1}-a_{n-2} \,\, for \,\, n > 2$$ It is further given that $a_4 = 194$ . Calculate $a_5$ .