A036928 Composite numbers whose prime factors contain no digits other than 0 and 1.
121, 1111, 1331, 10201, 12221, 14641, 111221, 112211, 134431, 161051, 1021211, 1030301, 1112221, 1223431, 1234321, 1478741, 1771561, 10212211, 11121011, 11233321, 11333311, 12101111, 12234431, 13457741, 13577531, 16266151
Offset: 1
Formula
Sum_{n>=1} 1/a(n) = Product_{p in A020449} (p/(p - 1)) - Sum_{p in A020449} 1/p - 1 = 0.0102023428... . - Amiram Eldar, May 18 2022
Extensions
Description clarified by Ray Chandler, Nov 07 2008