Numbers k such that phi(k-1) + phi(k+1) = sigma(k)/2.

Terms

a(0) =315a(1) =351a(2) =819a(3) =3375a(4) =24921a(5) =47520a(6) =99540a(7) =107541a(8) =125631a(9) =189175a(10) =410805a(11) =763665a(12) =877365a(13) =1680855a(14) =2480555a(15) =6911079a(16) =7849479a(17) =9646395a(18) =11245365a(19) =12528165a(20) =14242800a(21) =14684055a(22) =16921191a(23) =17194365a(24) =19395025a(25) =27782160a(26) =33830685a(27) =34823075a(28) =36278649a(29) =43955955