A036314 - OEIS

%I #23 May 22 2022 05:47:40

%S 9,27,81,129,243,387,729,1161,1299,1329,1849,2187,3483,3897,3987,5547,

%T 6561,10029,10299,10449,11691,11961,16641,18619,19049,19683,30087,

%U 30897,31347,35073,35883,49923,55857,57147,59049,79507,90261,92691

%N Composite numbers whose prime factors contain no digits other than 3 and 4.

%C All terms are a product of at least two terms of A020461. - _David A. Corneth_, Oct 09 2020

%H David A. Corneth, <a href="/A036314/b036314.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 A020461} (p/(p - 1)) - Sum_{p in A020461} 1/p - 1 = 0.1819438988... . - _Amiram Eldar_, May 22 2022

%Y Cf. A020461, A036302-A036325.

%K nonn,easy,base

%O 1,1

%A _Patrick De Geest_, Dec 15 1998