A036322 - OEIS

%I #25 May 22 2022 05:49:50

%S 49,343,469,2401,3283,4489,4739,16807,22981,31423,33173,45359,117649,

%T 160867,219961,232211,300763,317513,458329,474439,536669,537439,

%U 823543,1126069,1539727,1625477,2105341,2222591,3039053,3208303,3321073

%N Composite numbers whose prime factors contain no digits other than 6 and 7.

%C The multiplicative closure of A020469 consists of itself, 1, and this sequence. - _Charles R Greathouse IV_, Jun 25 2014

%H David A. Corneth, <a href="/A036322/b036322.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 A020469} (p/(p - 1)) - Sum_{p in A020469} 1/p - 1 = 0.0268448443... . - _Amiram Eldar_, May 22 2022

%Y Cf. A020469, A036302-A036325.

%K nonn,easy,base

%O 1,1

%A _Patrick De Geest_, Dec 15 1998