a(n) = 2*a(n-1) + a(n-2) + a(n-3) + a(n-4), a(0)=4, a(1)=2, a(2)=6, a(3)=17.

Terms

a(0) =4a(1) =2a(2) =6a(3) =17a(4) =46a(5) =117a(6) =303a(7) =786a(8) =2038a(9) =5282a(10) =13691a(11) =35488a(12) =91987a(13) =238435a(14) =618036a(15) =1601982a(16) =4152422a(17) =10763297a(18) =27899034a(19) =72315769a(20) =187446291a(21) =485870682a(22) =1259402458a(23) =3264437658a(24) =8461594747a(25) =21932900292a(26) =56851235447a(27) =147361403591a(28) =381968537668a(29) =990082614666