Numbers m such that sigma(m-1) is a prime.

Terms

a(0) =3a(1) =5a(2) =10a(3) =17a(4) =26a(5) =65a(6) =290a(7) =730a(8) =1682a(9) =2402a(10) =3482a(11) =4097a(12) =5042a(13) =7922a(14) =10202a(15) =15626a(16) =17162a(17) =27890a(18) =28562a(19) =29930a(20) =65537a(21) =83522a(22) =85850a(23) =146690a(24) =262145a(25) =279842a(26) =458330a(27) =491402a(28) =531442a(29) =552050