Primes of the form: 1 + sigma(n)^4.

Terms

a(0) =2a(1) =257a(2) =1297a(3) =614657a(4) =331777a(5) =331777a(6) =160001a(7) =331777a(8) =9834497a(9) =5308417a(10) =8503057a(11) =5308417a(12) =9834497a(13) =65610001a(14) =5308417a(15) =8503057a(16) =40960001a(17) =65610001a(18) =29986577a(19) =384160001a(20) =40960001a(21) =303595777a(22) =1049760001a(23) =65610001a(24) =1944810001a(25) =3782742017a(26) =1944810001a(27) =1049760001