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%I #17 Sep 24 2020 04:09:14
%S 1,5,9,25,45,81,125,225,405,625,729,1125,2025,3125,3645,5625,6561,
%T 10125,15625,18225,28125,32805,50625,59049,78125,91125,140625,164025,
%U 253125,295245,390625,455625,531441,703125,820125,1265625,1476225,1953125
%N Numbers of form 5^i*9^j, with i, j >= 0.
%H Amiram Eldar, <a href="/A025624/b025624.txt">Table of n, a(n) for n = 1..10000</a>
%F Sum_{n>=1} 1/a(n) = (5*9)/((5-1)*(9-1)) = 45/32. - _Amiram Eldar_, Sep 24 2020
%F a(n) ~ exp(sqrt(2*log(5)*log(9)*n)) / sqrt(45). - _Vaclav Kotesovec_, Sep 24 2020
%t f[upto_]:=Module[{maxi=Ceiling[Log[5,upto]],maxj=Ceiling[Log[9,upto]],s}, s=Union[Flatten[Outer[Times,5^Range[0,maxi], 9^Range[0,maxj]]]]; Select[s,#<=upto&]]; f[2000000] (* _Harvey P. Dale_, Mar 27 2011 *)
%Y Subsequence of A003593.
%K easy,nonn
%O 1,2
%A _David W. Wilson_
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