This is a left inverse of A304755, and also the right inverse if A304755 is a permutation of natural numbers, in which case the fallback clause is unnecessary.
Table of n, a(n) for n=1..42.
For n >= 1, a(A304755(n)) = n.
(PARI) \\ Use the program given in A304755.
Cf. A304755 (inverse).
Sequence in context: A195328 A294447 A143085 * A005227 A185185 A234019
Adjacent sequences: A304753 A304754 A304755 * A304757 A304758 A304759
Antti Karttunen, May 20 2018