Position of n-th 5 in A031312.

Terms

a(0) =3a(1) =11a(2) =21a(3) =31a(4) =41a(5) =46a(6) =48a(7) =50a(8) =51a(9) =52a(10) =54a(11) =61a(12) =71a(13) =81a(14) =91a(15) =104a(16) =119a(17) =134a(18) =149a(19) =164a(20) =172a(21) =175a(22) =178a(23) =179a(24) =181a(25) =184a(26) =194a(27) =209a(28) =224a(29) =239