(n-1)-st elementary symmetric function of the first n terms of (3,1,2,3,1,2,3,1,2,...).

Terms

a(0) =1a(1) =4a(2) =11a(3) =39a(4) =57a(5) =132a(6) =432a(7) =540a(8) =1188a(9) =3780a(10) =4428a(11) =9504a(12) =29808a(13) =33696a(14) =71280a(15) =221616a(16) =244944a(17) =513216a(18) =1586304a(19) =1726272a(20) =3592512a(21) =11057472a(22) =11897280a(23) =24634368a(24) =75582720a(25) =80621568a(26) =166281984a(27) =508923648a(28) =539156736a(29) =1108546560