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Composite numbers whose prime factors contain no digits other than 1 and 4.
2

%I #28 May 18 2022 07:56:00

%S 121,451,1331,1681,4961,14641,18491,45221,48851,54571,68921,125521,

%T 158521,161051,168551,182081,203401,452551,455521,467851,485221,

%U 497431,537361,590851,600281,758131,1380731,1686781,1697851,1743731,1771561

%N Composite numbers whose prime factors contain no digits other than 1 and 4.

%C All terms are a product of at least two terms of A020452. - _David A. Corneth_, Oct 09 2020

%H David A. Corneth, <a href="/A036304/b036304.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 A020452} (p/(p - 1)) - Sum_{p in A020452} 1/p - 1 = 0.0122909749... . - _Amiram Eldar_, May 18 2022

%e The composite 4961 = 11^2 * 41 is in the sequence as the digits of its prime factors are either 1 or 4. - _David A. Corneth_, Oct 17 2020

%Y Cf. A020452, A036302-A036325.

%K nonn,easy,base

%O 1,1

%A _Patrick De Geest_, Dec 15 1998