a(0)=a(1)=1, a(2)=4, a(3)=7, a(n+4) = 10*a(n+2) - a(n).

Terms

a(0) =1a(1) =1a(2) =4a(3) =7a(4) =39a(5) =69a(6) =386a(7) =683a(8) =3821a(9) =6761a(10) =37824a(11) =66927a(12) =374419a(13) =662509a(14) =3706366a(15) =6558163a(16) =36689241a(17) =64919121a(18) =363186044a(19) =642633047a(20) =3595171199a(21) =6361411349a(22) =35588525946a(23) =62971480443a(24) =352290088261a(25) =623353393081