a(n) = binomial(n+1, 2)^5.

Terms

a(0) =1a(1) =243a(2) =7776a(3) =100000a(4) =759375a(5) =4084101a(6) =17210368a(7) =60466176a(8) =184528125a(9) =503284375a(10) =1252332576a(11) =2887174368a(12) =6240321451a(13) =12762815625a(14) =24883200000a(15) =46525874176a(16) =83841135993a(17) =146211169851a(18) =247609900000a(19) =408410100000a(20) =657748550151