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 A062180 #7 Apr 05 2021 21:07:56 %S A062180 2,22,136,144,163,222,316,361,414,441,613,631,1236,1244,1263,1326, %T A062180 1333,1362,1424,1442,1623,1632,2136,2144,2163,2222,2316,2361,2414, %U A062180 2441,2613,2631,3126,3133,3162,3216,3261,3313,3331,3612,3621,4124,4142,4214,4241 %N A062180 Harmonic mean of digits is 2. %H A062180 Robert Israel, <a href="/A062180/b062180.txt">Table of n, a(n) for n = 1..10000</a> %p A062180 h:= proc(L) local m,x,i,t; %p A062180 m:= nops(L)+1; %p A062180 x:= m/2 - add(1/t, t=L); %p A062180 if x > 0 then %p A062180 x:= 1/x; %p A062180 if x::posint and x <= 9 then %p A062180 return(x + add(L[i]*10^i,i=1..m-1)) %p A062180 fi fi %p A062180 end proc: %p A062180 f:= n -> h(map(`+`,convert(n,base,9),1)): %p A062180 g:= n -> h([op(map(`+`,convert(n,base,9),1)),1]): %p A062180 R:= 2: %p A062180 for d from 1 to 4 do %p A062180 R:= R, seq(f(i),i=9^(d-1)..9^d-1),seq(g(i),i=9^(d-1)..9^d-1) %p A062180 od: %p A062180 R; # _Robert Israel_, Apr 05 2021 %t A062180 Do[ h = IntegerDigits[n]; If[ Sort[h][[1]] != 0 && Length[h]/Apply[Plus, 1/h] == 2, Print[n]], {n, 1, 10^4}] %Y A062180 Cf. A062179-A062185, A061383-A061388, A061423-A061425. %K A062180 base,easy,nonn %O A062180 1,1 %A A062180 _Vladeta Jovovic_, Jun 12 2001 %E A062180 More terms from _Henry Bottomley_, Jul 25 2001