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%I #18 Sep 23 2020 03:54:30
%S 1,2,4,5,7,8,10,14,16,20,25,28,32,35,40,49,50,56,64,70,80,98,100,112,
%T 125,128,140,160,175,196,200,224,245,250,256,280,320,343,350,392,400,
%U 448,490,500,512,560,625,640,686,700,784,800,875,896,980,1000,1024,1120
%N Numbers of the form (2^i)*(5^j)*(7^k), with i, j, k >= 0.
%C Numbers m | 70^e with integer e >= 0. - _Michael De Vlieger_, Aug 22 2019
%H Michael De Vlieger, <a href="/A108513/b108513.txt">Table of n, a(n) for n = 1..10000</a>
%F Sum_{n>=1} 1/a(n) = (2*5*7)/((2-1)*(5-1)*(7-1)) = 35/12. - _Amiram Eldar_, Sep 23 2020
%F a(n) ~ exp((6*log(2)*log(5)*log(7)*n)^(1/3)) / sqrt(70). - _Vaclav Kotesovec_, Sep 23 2020
%t With[{n = 1120}, Sort@ Flatten@ Table[2^i * 5^j * 7^k, {i, 0, Log2@ n}, {j, 0, Log[5, n/2^i]}, {k, 0, Log[7, n/(2^i*5^j)]}]] (* _Michael De Vlieger_, Aug 22 2019 *)
%o (PARI) isok(n) = (n/(2^valuation(n,2)*5^valuation(n,5)*7^valuation(n,7)) == 1); \\ _Michel Marcus_, Oct 01 2013
%Y Cf. A051037, A108319, A108347, A003592, A003591, A003595.
%K nonn,easy
%O 1,2
%A Douglas Winston (douglas.winston(AT)srupc.com), Jul 05 2005
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