%I #13 Sep 23 2020 03:03:49

%S 1,2,3,4,5,6,8,9,10,12,16,18,20,24,25,27,32,36,40,48,50,54,64,72,80,

%T 81,96,100,108,125,128,144,160,162,192,200,216,243,250,256,288,320,

%U 324,384,400,432,486,500,512,576,625,640,648,729,768,800,864,972,1000

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

%C Union of A003586 and A003592.

%H Vaclav Kotesovec, <a href="/A337800/b337800.txt">Table of n, a(n) for n = 1..10000</a>

%H Vaclav Kotesovec, <a href="/A337800/a337800.jpg">Graph - the asymptotic ratio (64000000 terms)</a>

%F a(n) ~ exp(sqrt(2*log(2)*log(3)*log(5)*n / log(15))) / sqrt(2).

%F Sum_{n>=1} 1/a(n) = 7/2. - _Amiram Eldar_, Sep 23 2020

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

%Y Cf. A003586, A003592, A257997, A258023, A337801.

%K nonn,easy

%O 1,2

%A _Vaclav Kotesovec_, Sep 22 2020