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 A063972 #10 Sep 22 2019 08:03:50
%S A063972 1,0,2,3,4,5,0,7,8,9,0,6,0,13,0,0,16,10,0,12,0,0,0,14,0,25,0,27,0,18,
%T A063972 0,21,32,0,0,22,0,37,0,28,0,26,0,43,0,0,0,33,0,36,0,0,0,34,0,39,0,0,0,
%U A063972 38,0,61,0,0,64,0,0,48,0,52,0,30,0,73,0,0,0,50,0,57,0,81,0,54,0,0,0,0,0
%N A063972 a(n) is the smallest m such that usigma(m) = n (or 0 if no such m).
%C A063972 usigma(m) is the sum of unitary divisors of m, A034448.
%H A063972 Amiram Eldar, <a href="/A063972/b063972.txt">Table of n, a(n) for n = 1..10000</a>
%e A063972 a(12)=6 because the unitary divisors of 6 are 1,2,3,6; they sum to 12.
%t A063972 usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); m = 100; v = Table[0, {m}]; Do[u = usigma[n]; If[u <= m && v[[u]] == 0, v[[u]] = n], {n, 1, m}]; v (* _Amiram Eldar_, Sep 22 2019 *)
%Y A063972 Cf. A034444, A034448, A051444, A057637, A063973.
%K A063972 nonn
%O A063972 1,3
%A A063972 _Labos Elemer_, Sep 05 2001
%E A063972 Edited by _Don Reble_, May 14 2006