a(n) = 4*a(n-1) + 1, a(1)=11.

Terms

a(0) =11a(1) =45a(2) =181a(3) =725a(4) =2901a(5) =11605a(6) =46421a(7) =185685a(8) =742741a(9) =2970965a(10) =11883861a(11) =47535445a(12) =190141781a(13) =760567125a(14) =3042268501a(15) =12169074005a(16) =48676296021a(17) =194705184085a(18) =778820736341