Numbers n such that sigma(n) and sigma(n^2) are primes.

Terms

a(0) =2a(1) =4a(2) =64a(3) =289a(4) =729a(5) =15625a(6) =7091569a(7) =7778521a(8) =11607649a(9) =15912121a(10) =43546801a(11) =56957209a(12) =138980521a(13) =143688169a(14) =171845881a(15) =210801361a(16) =211673401a(17) =253541929a(18) =256224049a(19) =275792449a(20) =308810329a(21) =329386201a(22) =357172201a(23) =408807961a(24) =499477801a(25) =531625249a(26) =769341169a(27) =1073741824a(28) =1260747049