A036315 - OEIS

%I #28 May 22 2022 05:51:46

%S 9,15,25,27,45,75,81,125,135,159,225,243,265,375,405,477,625,675,729,

%T 795,1059,1125,1215,1325,1431,1765,1875,2025,2187,2385,2809,3125,3177,

%U 3375,3645,3975,4293,5295,5625,6075,6561,6625,7155,8427,8825,9375,9531

%N Composite numbers whose prime factors contain no digits other than 3 and 5.

%C Products of at least two terms of A020462. - _David A. Corneth_, Oct 09 2020

%H David A. Corneth, <a href="/A036315/b036315.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 A020462} (p/(p - 1)) - Sum_{p in A020462} 1/p - 1 = 0.3620363317... . - _Amiram Eldar_, May 22 2022

%t Select[Range[10000],SubsetQ[{3,5},Union[Flatten[IntegerDigits/@ FactorInteger[ #][[All,1]]]]]&&CompositeQ[#]&] (* _Harvey P. Dale_, May 30 2021 *)

%Y Cf. A003593, A020462, A036302-A036325.

%K nonn,easy,base

%O 1,1

%A _Patrick De Geest_, Dec 15 1998