This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A324921 #16 May 08 2019 15:48:57
%S A324921 0,1,2,3,10,11,26,83,178,179,362,1835,9188,42709,162466,358487,
%T A324921 1877938,11596979,57866702,94418279,1888365980
%N A324921 Index of first occurrence of n in A324920.
%t A324921 g[n_] := Block[{d = Divisors@ n}, len = Length@ d; If[ OddQ@ len, 0, d[[1 + len/2]] - d[[len/2]]]]; f[n_] := Length@ NestWhileList[g, n, # > 0 &] - 1; t[_] := -1; k = 0; While[k < 1000000001, a = f@ k; If[ t[a] == -1, t[a] = k]; k++]; t@# & /@ Range[0, 17]
%o A324921 (PARI) a056737(n)=n=divisors(n); n[(2+#n)\2]-n[(1+#n)\2] \\ after _M. F. Hasler_ in A056737
%o A324921 a324920(n) = my(x=n, i=0); while(x!=0, i++; x=a056737(x)); i
%o A324921 a(n) = for(k=0, oo, if(a324920(k)==n, return(k))) \\ _Felix Fröhlich_, Mar 20 2019
%Y A324921 Cf. A056737, A324920.
%K A324921 nonn,more
%O A324921 0,3
%A A324921 _Robert G. Wilson v_, Mar 20 2019
%E A324921 a(18)-a(20) from _Daniel Suteu_, Mar 20 2019