Numbers n such that sigma(n-1) and sigma(n) - 1 are both primes.

Terms

a(0) =3a(1) =5a(2) =10a(3) =17a(4) =26a(5) =65a(6) =65537a(7) =146690a(8) =703922a(9) =1481090a(10) =1885130a(11) =2036330a(12) =2211170a(13) =2430482a(14) =2505890a(15) =5470922a(16) =9840770a(17) =11607650a(18) =17783090a(19) =24137570a(20) =74425130a(21) =76615010a(22) =77563250a(23) =133379402a(24) =138697730a(25) =138980522a(26) =142396490a(27) =155575730a(28) =177715562a(29) =181899170