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 A193572 #18 Feb 16 2025 08:33:15 %S A193572 20,24,204,224,240,242,402,420,422,1133,1313,1331,2004,2024,2040,2042, %T A193572 2204,2240,2400,2402,2420,3113,3131,3311,4002,4020,4022,4200,4202, %U A193572 4220,4899,4989,4998,5779,5797,5977,7579,7597,7759,7795,7957,7975,8499,8949,8994 %N A193572 Unhappy numbers which enter the cycle (4, 16, 37, 58, 89, 145, 42, 20) at 20. %H A193572 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/UnhappyNumber.html">Unhappy Number</a>. %e A193572 4899 is such a number of height 3 because it enters the cycle at 20 in 3 steps: 4899 -> 242 -> 24 -> 20 -> 4 -> 16 -> 37 -> 58 -> 89 -> 145 -> 42 -> 20 -> ... %p A193572 S:=proc(n) local Q,k,N,z; Q:=[n]; for k from 1 do N:=convert(Q[k],base,10); z:=sum(N['i']^2,'i'=1..nops(N)); if not member(z,Q) then Q:=[op(Q),z]; else Q:=[op(Q),z]; break; fi; od; return Q; end: %p A193572 a:=[]: for i from 1 while nops(a)<30 do Q:=S(i); A:=Q[nops(Q)]; if A=20 then a:=[op(a),i] fi; od: print(op(a)); %Y A193572 Cf. A031177, A039943. %K A193572 nonn,base %O A193572 1,1 %A A193572 _Martin Renner_, Jul 31 2011