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%I #29 May 18 2022 07:56:07
%S 121,671,1331,3721,7271,7381,14641,40321,40931,73271,79981,81191,
%T 122771,161051,177221,183271,226981,406321,436921,443531,450241,
%U 680821,727771,805981,879791,893101,982771,1016321,1227721,1350481,1771561
%N Composite numbers whose prime factors contain no digits other than 1 and 6.
%C All terms are a product of at least two terms of A020454. - _David A. Corneth_, Oct 09 2020
%H David A. Corneth, <a href="/A036306/b036306.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Alois P. Heinz)
%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 A020454} (p/(p - 1)) - Sum_{p in A020454} 1/p - 1 = 0.0112607346... . - _Amiram Eldar_, May 18 2022
%t pf16Q[n_]:=Module[{pfs=Union[Flatten[IntegerDigits/@Transpose[ FactorInteger[ n]][[1]]]]},pfs=={1}||pfs=={1,6}]; Select[Range[ 2*10^6],CompositeQ[#]&&pf16Q[#]&] (* _Harvey P. Dale_, Jul 12 2014 *)
%Y Cf. A020454, A036302-A036325.
%K nonn,easy,base
%O 1,1
%A _Patrick De Geest_, Dec 15 1998
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