A131097 - OEIS

%I #12 Sep 17 2019 18:34:03

%S 1,2,1,2,2,4,1,2,4,2,4,1,4,2,4,2,4,4,1,4,2,6,4,2,4,4,1,4,4,2,6,4,2,8,

%T 4,4,1,4,4,2,8,6,4,2,8,4,4,10,1,4,4,2,8,6,4,10,2,8,4,4,10,1,4,4,8,2,8,

%U 6,4,10,2,8,4,10,4,10,1,4,4,8,2,8,6,16,4,10,2,8,4,10,4

%N Sum of digits of 3-smooth numbers in ternary representation.

%C a(n) = A053735(A003586(n)); values are even iff greater than 1.

%H Robert Israel, <a href="/A131097/b131097.txt">Table of n, a(n) for n = 1..10000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/DigitSum.html">Digit Sum</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Ternary.html">Ternary</a>

%p Res:= NULL: N:= 10^6:

%p for a from 0 to ilog2(N) do

%p   for b from 0 do

%p     v:= 2^a*3^b;

%p     if v > N then break fi;

%p     Res:= Res, v;

%p od od:

%p TS:= sort([Res]):

%p map(t -> convert(convert(t,base,3),`+`), TS); # _Robert Israel_, Oct 08 2018

%K nonn,base,look

%O 1,2

%A _Reinhard Zumkeller_, Jun 14 2007