a(n) = 10*4^n+1.

Terms

a(0) =11a(1) =41a(2) =161a(3) =641a(4) =2561a(5) =10241a(6) =40961a(7) =163841a(8) =655361a(9) =2621441a(10) =10485761a(11) =41943041a(12) =167772161a(13) =671088641a(14) =2684354561a(15) =10737418241a(16) =42949672961a(17) =171798691841a(18) =687194767361