OFFSET
1,1
COMMENTS
All terms are a product of at least two terms of A020470. - David A. Corneth, Oct 09 2020
LINKS
FORMULA
Sum_{n>=1} 1/a(n) = Product_{p in A020470} (p/(p - 1)) - Sum_{p in A020470} 1/p - 1 = 0.0244618735... . - Amiram Eldar, May 22 2022
MATHEMATICA
Select[Range[25*10^5], CompositeQ[#]&&SubsetQ[{7, 8}, Flatten[ IntegerDigits/@ Transpose[ FactorInteger[#]][[1]]]]&] (* Harvey P. Dale, Jan 19 2015 *)
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
Patrick De Geest, Dec 15 1998
STATUS
approved