a(n) = 2*a(n-1) + 7*a(n-2) for n > 1; a(0) = 1, a(1) = 7.

Terms

a(0) =1a(1) =7a(2) =21a(3) =91a(4) =329a(5) =1295a(6) =4893a(7) =18851a(8) =71953a(9) =275863a(10) =1055397a(11) =4041835a(12) =15471449a(13) =59235743a(14) =226771629a(15) =868193459a(16) =3323788321a(17) =12724930855a(18) =48716379957a(19) =186507275899a(20) =714029211497