cp's OEIS Frontend

A281004 Numbers with exactly 3 ones in both binary and ternary representations.

%I A281004 #8 Jan 12 2017 20:13:59
%S A281004 13,37,41,49,67,97,131,133,145,193,259,265,273,289,385,517,529,577,
%T A281004 1027,1029,1033,1041,1153,1281,2053,2057,4101,4105,4113,4129,4161,
%U A281004 6145,8195,8197,8209,8225,8257,8321,8449,8705,10241,16449,17409,18433,20481,24577,32771,32777,32785,32801,32833,32897
%N A281004 Numbers with exactly 3 ones in both binary and ternary representations.
%C A281004 Intersection of A014311 and A023694.
%C A281004 All terms are odd, since n == A062756(n) (mod 2).
%C A281004 It is likely that a(136) = 1099528404993 is the last term.  The next term, if any, is greater than 10^200.
%H A281004 Robert Israel, <a href="/A281004/b281004.txt">Table of n, a(n) for n = 1..136</a>
%e A281004 a(4) = 49 = 110001_2 = 1211_3.
%p A281004 R:= NULL: count:= 0:
%p A281004 for a from 2 while count < 136 do
%p A281004   for b from 1 to a-1  do
%p A281004     p:= 2^a + 2^b + 1;
%p A281004     if numboccur(1, convert(p,base,3)) = 3 then
%p A281004       count:= count+1;
%p A281004       R:= R, p;
%p A281004     fi
%p A281004 od od:
%p A281004 R;
%Y A281004 Cf. A014311, A023694, A062756.  Contains A280997.
%K A281004 nonn,base
%O A281004 1,1
%A A281004 _Robert Israel_, Jan 12 2017