OFFSET
1,1
COMMENTS
All terms are a product of at least two terms of A020452. - David A. Corneth, Oct 09 2020
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000 (first 1000 terms from Alois P. Heinz)
FORMULA
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
EXAMPLE
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
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
Patrick De Geest, Dec 15 1998
STATUS
approved