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

Terms

a(0) =4a(1) =6a(2) =11a(3) =32a(4) =38a(5) =54a(6) =84a(7) =278a(8) =407a(9) =804a(10) =1854a(11) =2664a(12) =3287a(13) =6579a(14) =11327a(15) =14750a(16) =15608a(17) =20720a(18) =41664a(19) =46839a(20) =70190a(21) =73283a(22) =80429a(23) =185231a(24) =241614a(25) =275876a(26) =355292a(27) =375200a(28) =410327a(29) =511220