a(n) = 10*a(n-2) - 16*a(n-4) for n>=4, with a(0)=a(1)=1, a(2)=6, a(3)=10.

Terms

a(0) =1a(1) =1a(2) =6a(3) =10a(4) =44a(5) =84a(6) =344a(7) =680a(8) =2736a(9) =5456a(10) =21856a(11) =43680a(12) =174784a(13) =349504a(14) =1398144a(15) =2796160a(16) =11184896a(17) =22369536a(18) =89478656a(19) =178956800a(20) =715828224a(21) =1431655424a(22) =5726623744a(23) =11453245440a(24) =45812985856a(25) =91625967616a(26) =366503878656