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A036317
Composite numbers whose prime factors contain no digits other than 3 and 8.
2
9, 27, 81, 243, 249, 729, 747, 1149, 2187, 2241, 2649, 3447, 6561, 6723, 6889, 7947, 10341, 11499, 19683, 20169, 20667, 23841, 31023, 31789, 34497, 59049, 60507, 62001, 71523, 73289, 93069, 95367, 103491, 114999, 116499, 146689, 177147
OFFSET
1,1
COMMENTS
All terms are a product of at least two terms of A020464. - David A. Corneth, Oct 09 2020
FORMULA
Sum_{n>=1} 1/a(n) = Product_{p in A020464} (p/(p - 1)) - Sum_{p in A020464} 1/p - 1 = 0.1750565813... . - Amiram Eldar, May 22 2022
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
Patrick De Geest, Dec 15 1998
STATUS
approved