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%I #24 May 22 2022 05:50:03
%S 49,343,2401,5509,6139,6209,16807,38563,42973,43463,55139,62209,
%T 117649,269941,300811,304241,385973,435463,551509,552139,552209,
%U 615139,615209,619369,690199,698069,769129,777899,786769,823543,1889587,2105677
%N Composite numbers whose prime factors contain no digits other than 7 and 8.
%C All terms are a product of at least two terms of A020470. - _David A. Corneth_, Oct 09 2020
%H David A. Corneth, <a href="/A036323/b036323.txt">Table of n, a(n) for n = 1..10000</a>
%H <a href="/index/Pri#prime_factors">Index entries for sequences related to prime factors</a>.
%F Sum_{n>=1} 1/a(n) = Product_{p in A020470} (p/(p - 1)) - Sum_{p in A020470} 1/p - 1 = 0.0244618735... . - _Amiram Eldar_, May 22 2022
%t Select[Range[25*10^5],CompositeQ[#]&&SubsetQ[{7,8},Flatten[ IntegerDigits/@ Transpose[ FactorInteger[#]][[1]]]]&] (* _Harvey P. Dale_, Jan 19 2015 *)
%Y Cf. A020470, A036302-A036325.
%K nonn,easy,base
%O 1,1
%A _Patrick De Geest_, Dec 15 1998
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