cp's OEIS Frontend

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.

A062180 Harmonic mean of digits is 2.

This page as a plain text file.
%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