A modular recurrence.

Terms

a(0) =1a(1) =5a(2) =15a(3) =75a(4) =225a(5) =1125a(6) =3375a(7) =16875a(8) =50625a(9) =253125a(10) =759375a(11) =3796875a(12) =11390625a(13) =56953125a(14) =170859375a(15) =854296875a(16) =2562890625a(17) =12814453125a(18) =38443359375a(19) =192216796875a(20) =576650390625