Least number k such that sigma_2(k) >= 2^n.

Terms

a(0) =2a(1) =2a(2) =3a(3) =4a(4) =6a(5) =8a(6) =10a(7) =15a(8) =20a(9) =28a(10) =40a(11) =54a(12) =78a(13) =108a(14) =156a(15) =216a(16) =300a(17) =420a(18) =600a(19) =840a(20) =1188a(21) =1680a(22) =2340a(23) =3360a(24) =4680a(25) =6600a(26) =9240a(27) =13200a(28) =18480a(29) =26400