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Numbers having more than three divisors that are also suffixes in binary representation.
3

%I #9 May 02 2014 00:25:07

%S 63,126,231,252,255,363,399,462,495,504,510,567,627,726,735,759,798,

%T 845,891,903,924,975,990,1008,1020,1023,1071,1134,1215,1239,1254,1365,

%U 1407,1419,1452,1455,1470,1518,1575,1596,1690,1695,1743,1755,1782,1806,1848

%N Numbers having more than three divisors that are also suffixes in binary representation.

%C A080942(a(n))>3.

%H Reinhard Zumkeller, <a href="/A080947/b080947.txt">Table of n, a(n) for n = 1..1000</a>

%e a(4) = 252: divisors(252) = {1, 2, 3, 4->'100', 6, 7, 9, 12->'1100', 14, 18, 21, 28->'11100', 36, 42, 63, 84, 126, 252->'11111100'}: A080946(252) = #{4, 12, 28, 252} = 4;

%e a(15) = 735: divisors(735) = {1->'1', 3->'11', 5, 7->'111', 15->'1111', 21, 35, 49, 105, 147, 245, 735->'1011011111'}: A080942(735) = #{1, 3, 7, 15, 735} = 5.

%o (Haskell)

%o a080947 n = a080947_list !! (n-1)

%o a080947_list = filter ((> 3) . a080942) [1..]

%o -- _Reinhard Zumkeller_, Mar 27 2014

%Y Cf. A080946, A007088, A080940, A080941.

%K nonn,base

%O 1,1

%A _Reinhard Zumkeller_, Feb 25 2003