a(n) = 6*5*4*3*2*1 + 12*11*10*9*8*7 + 18*17*16*15*14*13 + ... + (up to the n-th term).

Terms

a(0) =6a(1) =30a(2) =120a(3) =360a(4) =720a(5) =720a(6) =732a(7) =852a(8) =2040a(9) =12600a(10) =95760a(11) =666000a(12) =666018a(13) =666306a(14) =670896a(15) =739440a(16) =1694160a(17) =14032080a(18) =14032104a(19) =14032632a(20) =14044224a(21) =14287104a(22) =19132560a(23) =110941200a(24) =110941230a(25) =110942070a(26) =110965560a(27) =111598920a(28) =128041920a(29) =538459200