%N Inverse function of N -> N injection A075173.
%C a(n) = 0 for those n which do not occur as the values of A075173. All positive natural numbers occur here once.
%Y a(A075173(n)) = n for all n >= 1. Differs from A075176 for first time at a(18) = 0, while A075176(18) = 9.
%A _Antti Karttunen_, Sep 13 2002