a(n) is the least k >= 2 such that (2^k - 1) mod (n*k - 1) = 0.

Terms

a(0) =2a(1) =2a(2) =12a(3) =4a(4) =24a(5) =216a(6) =792a(7) =32a(8) =144a(9) =4410a(10) =396a(11) =108a(12) =208a(13) =1880a(14) =3192a(15) =16a(16) =9240a(17) =72a(18) =24a(19) =6048a(20) =264a(21) =2160a(22) =1872a(23) =270a(24) =20916a(25) =104a(26) =5292a(27) =940a(28) =360a(29) =1596