A281004 - OEIS

%I #8 Jan 12 2017 20:13:59

%S 13,37,41,49,67,97,131,133,145,193,259,265,273,289,385,517,529,577,

%T 1027,1029,1033,1041,1153,1281,2053,2057,4101,4105,4113,4129,4161,

%U 6145,8195,8197,8209,8225,8257,8321,8449,8705,10241,16449,17409,18433,20481,24577,32771,32777,32785,32801,32833,32897

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

%C Intersection of A014311 and A023694.

%C All terms are odd, since n == A062756(n) (mod 2).

%C It is likely that a(136) = 1099528404993 is the last term.  The next term, if any, is greater than 10^200.

%H Robert Israel, <a href="/A281004/b281004.txt">Table of n, a(n) for n = 1..136</a>

%e a(4) = 49 = 110001_2 = 1211_3.

%p R:= NULL: count:= 0:

%p for a from 2 while count < 136 do

%p   for b from 1 to a-1  do

%p     p:= 2^a + 2^b + 1;

%p     if numboccur(1, convert(p,base,3)) = 3 then

%p       count:= count+1;

%p       R:= R, p;

%p     fi

%p od od:

%p R;

%Y Cf. A014311, A023694, A062756.  Contains A280997.

%K nonn,base

%O 1,1

%A _Robert Israel_, Jan 12 2017