Companion Pell numbers: a(n) = 2*a(n-1) + a(n-2), a(0) = a(1) = 2.

Terms

a(0) =2a(1) =2a(2) =6a(3) =14a(4) =34a(5) =82a(6) =198a(7) =478a(8) =1154a(9) =2786a(10) =6726a(11) =16238a(12) =39202a(13) =94642a(14) =228486a(15) =551614a(16) =1331714a(17) =3215042a(18) =7761798a(19) =18738638a(20) =45239074a(21) =109216786a(22) =263672646a(23) =636562078a(24) =1536796802a(25) =3710155682a(26) =8957108166a(27) =21624372014a(28) =52205852194a(29) =126036076402