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A025611 Numbers of form 2^i*9^j, with i, j >= 0. 3

%I

%S 1,2,4,8,9,16,18,32,36,64,72,81,128,144,162,256,288,324,512,576,648,

%T 729,1024,1152,1296,1458,2048,2304,2592,2916,4096,4608,5184,5832,6561,

%U 8192,9216,10368,11664,13122,16384,18432,20736,23328,26244,32768,36864,41472

%N Numbers of form 2^i*9^j, with i, j >= 0.

%H Robert Israel, <a href="/A025611/b025611.txt">Table of n, a(n) for n = 1..10000</a>

%F Sum_{n>=1} 1/a(n) = (2*9)/((2-1)*(9-1)) = 9/4. - _Amiram Eldar_, Sep 24 2020

%F a(n) ~ exp(sqrt(2*log(2)*log(9)*n)) / sqrt(18). - _Vaclav Kotesovec_, Sep 24 2020

%p N:= 10^5: # for terms <= N

%p sort([seq(seq(2^i*9^j,i=0..ilog2(N/9^j)),j=0..floor(log[9](N)))]); # _Robert Israel_, Mar 23 2020

%t Take[Union[2^First[#] 9^Last[#]&/@Tuples[Range[0,20],{2}]],50] (* _Harvey P. Dale_, May 26 2011 *)

%t n = 10^5; Flatten[Table[2^i*9^j, {i, 0, Log[2, n]}, {j, 0, Log[9, n/2^i]}]] // Sort (* _Amiram Eldar_, Sep 24 2020 *)

%Y Subsequence of A003586.

%K easy,nonn

%O 1,2

%A _David W. Wilson_

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Last modified August 11 08:05 EDT 2022. Contains 356055 sequences. (Running on oeis4.)