%I #14 Sep 23 2020 03:04:11

%S 1,2,3,4,5,8,9,10,15,16,20,25,27,32,40,45,50,64,75,80,81,100,125,128,

%T 135,160,200,225,243,250,256,320,375,400,405,500,512,625,640,675,729,

%U 800,1000,1024,1125,1215,1250,1280,1600,1875,2000,2025,2048,2187,2500

%N Numbers of the form (2^i)*(5^j) or (3^i)*(5^j).

%C Union of A003592 and A003593.

%H Vaclav Kotesovec, <a href="/A337801/b337801.txt">Table of n, a(n) for n = 1..10000</a>

%H Vaclav Kotesovec, <a href="/A337801/a337801.jpg">Graph - the asymptotic ratio (42000000 terms)</a>

%F a(n) ~ exp(sqrt(2*log(2)*log(3)*log(5)*n / log(6))) / sqrt(5).

%F Sum_{n>=1} 1/a(n) = 25/8. - _Amiram Eldar_, Sep 23 2020

%t n = 10^4; Join[Table[2^i*5^j, {i, 0, Log[2, n]}, {j, 0, Log[5, n/2^i]}], Table[3^i*5^j, {i, 0, Log[3, n]}, {j, 0, Log[5, n/3^i]}]] // Flatten // Union (* _Amiram Eldar_, Sep 23 2020 *)

%Y Cf. A003592, A003593, A257997, A258023, A337800.

%K nonn,easy

%O 1,2

%A _Vaclav Kotesovec_, Sep 22 2020