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%I #28 May 18 2022 07:56:13
%S 121,1331,1991,8921,9691,12991,14641,19921,21901,32761,89221,98131,
%T 106601,142901,146791,159461,161051,199991,213761,219131,240911,
%U 327791,360371,657721,714491,776161,892991,957791,976921,981431,1040461,1079441,1172611,1394761,1468091
%N Composite numbers whose prime factors contain no digits other than 1 and 8.
%C All terms are a product of at least two terms of A020456. - _David A. Corneth_, Oct 09 2020
%H David A. Corneth, <a href="/A036308/b036308.txt">Table of n, a(n) for n = 1..10000</a> (first 58 terms from Vincenzo Librandi)
%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 A020456} (p/(p - 1)) - Sum_{p in A020456} 1/p - 1 = 0.0101097220... . - _Amiram Eldar_, May 18 2022
%t dpfQ[n_]:=Module[{d=Union[Flatten[IntegerDigits/@Transpose[FactorInteger[n]][[1]]]]}, !PrimeQ[n]&&(d == {1}||d == {8}||d == {1, 8})]; Select[Range[2, 1500000], dpfQ] (* _Vincenzo Librandi_, Aug 25 2013 *)
%o (Magma) [n: n in [4..1500000] | not IsPrime(n) and forall{f: f in PrimeDivisors(n) | Intseq(f) subset [1,8]}]; // _Bruno Berselli_, Aug 26 2013
%Y Cf. A020456, A036302-A036325.
%K nonn,easy,base
%O 1,1
%A _Patrick De Geest_, Dec 15 1998
%E More terms from _Vincenzo Librandi_, Aug 25 2013
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