a(n) is the least k such that A161606(k) = n or a(n) = -1 if no such k exists.

Terms

a(0) =1a(1) =2a(2) =4a(3) =27a(4) =84a(5) =48a(6) =336a(7) =320a(8) =2112a(9) =1792a(10) =3840a(11) =26112a(12) =21504a(13) =45056a(14) =143360a(15) =212992a(16) =540672a(17) =1720320a(18) =2555904a(19) =4456448a(20) =17039360a(21) =19922944a(22) =53447376a(23) =204472320a(24) =239075328a(25) =385875968a(26) =1593835520a(27) =4278190080a(28) =4630511616a(29) =19126026240