a(n) = 2n*a(n-1) + 1 with a(0)=0.

Terms

a(0) =0a(1) =1a(2) =5a(3) =31a(4) =249a(5) =2491a(6) =29893a(7) =418503a(8) =6696049a(9) =120528883a(10) =2410577661a(11) =53032708543