Tetranacci sequence beginning with 3, 7, 12, 24.

Terms

a(0) =3a(1) =7a(2) =12a(3) =24a(4) =46a(5) =89a(6) =171a(7) =330a(8) =636a(9) =1226a(10) =2363a(11) =4555a(12) =8780a(13) =16924a(14) =32622a(15) =62881a(16) =121207a(17) =233634a(18) =450344a(19) =868066a(20) =1673251a(21) =3225295a(22) =6216956a(23) =11983568a(24) =23099070a(25) =44524889a(26) =85824483a(27) =165432010a(28) =318880452a(29) =614661834