a(n)= 3*a(n-1) +2*a(n-2) +a(n-3).

Terms

a(0) =1a(1) =0a(2) =2a(3) =7a(4) =25a(5) =91a(6) =330a(7) =1197a(8) =4342a(9) =15750a(10) =57131a(11) =207235a(12) =751717a(13) =2726752a(14) =9890925a(15) =35877996a(16) =130142590a(17) =472074687a(18) =1712387237a(19) =6211453675a(20) =22531210186a(21) =81728925145a(22) =296460649482