a(n) = 3*a(n-1) - 2*a(n-2) - a(n-3), with a(0)=1, a(1)=3 and a(2)=7.

Terms

a(0) =1a(1) =3a(2) =7a(3) =14a(4) =25a(5) =40a(6) =56a(7) =63a(8) =37a(9) =-71a(10) =-350a(11) =-945a(12) =-2064a(13) =-3952a(14) =-6783a(15) =-10381a(16) =-13625a(17) =-13330a(18) =-2359a(19) =33208a(20) =117672a(21) =288959a(22) =598325a(23) =1099385a(24) =1812546a(25) =2640543a(26) =3197152a(27) =2497824a(28) =-1541375a(29) =-12816925