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A036320 Composite numbers whose prime factors contain no digits other than 5 and 7. 2
25, 35, 49, 125, 175, 245, 343, 625, 875, 1225, 1715, 2401, 2785, 2885, 3125, 3785, 3899, 4039, 4375, 5299, 6125, 8575, 12005, 13925, 14425, 15625, 16807, 18925, 19495, 20195, 21875, 26495, 27293, 27785, 28273, 30625, 37093, 37885, 38785 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
All terms are a product of at least two terms of A020467. - David A. Corneth, Oct 09 2020
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000
Index entries for sequences related to prime factors.
FORMULA
Sum_{n>=1} 1/a(n) = Product_{p in A020467} (p/(p - 1)) - Sum_{p in A020467} 1/p - 1 = 0.1179595738... . - Amiram Eldar, May 22 2022
CROSSREFS
Cf. A003595, A020467, A036302-A036325.
Sequence in context: A107472 A193165 A060976 * A339520 A340096 A348423
Adjacent sequences: A036317 A036318 A036319 * A036321 A036322 A036323
KEYWORD
nonn,easy,base
AUTHOR
Patrick De Geest, Dec 15 1998
STATUS
approved

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Last modified August 18 19:26 EDT 2024. Contains 375273 sequences. (Running on oeis4.)