Let m = A013929(n); then a(n) = smallest k such that m divides k^4.

Terms

a(0) =2a(1) =2a(2) =3a(3) =6a(4) =2a(5) =6a(6) =10a(7) =6a(8) =5a(9) =3a(10) =14a(11) =4a(12) =6a(13) =10a(14) =22a(15) =15a(16) =6a(17) =7a(18) =10a(19) =26a(20) =6a(21) =14a(22) =30a(23) =21a(24) =4a(25) =34a(26) =6a(27) =15a(28) =38a(29) =10