Position of the second n in A026400.

Terms

a(0) =4a(1) =6a(2) =10a(3) =12a(4) =14a(5) =19a(6) =23a(7) =28a(8) =35a(9) =36a(10) =42a(11) =44a(12) =58a(13) =60a(14) =67a(15) =73a(16) =78a(17) =86a(18) =94a(19) =98a(20) =109a(21) =126a(22) =127a(23) =143a(24) =144a(25) =156a(26) =158a(27) =171a(28) =190a(29) =207