Benjamin Chaffin, Table of n, a(n) for n=0..1000000. This represents the inverse of the first 3.2*10^11 terms of A274468. The 33242 entries of -1 correspond to values which have not yet appeared. The first missing number is 154. The largest term in this range is a(4287)=257890387560.

FORMULA

a(n) = index of n in A274648; for all n >= 0, a(A274648(n)) = n.