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A036304 Composite numbers whose prime factors contain no digits other than 1 and 4. 2
121, 451, 1331, 1681, 4961, 14641, 18491, 45221, 48851, 54571, 68921, 125521, 158521, 161051, 168551, 182081, 203401, 452551, 455521, 467851, 485221, 497431, 537361, 590851, 600281, 758131, 1380731, 1686781, 1697851, 1743731, 1771561 (list; graph; refs; listen; history; text; internal format)
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
Sequence in context: A144719 A222551 A017282 * A052082 A062555 A017390
KEYWORD
nonn,easy,base
AUTHOR
Patrick De Geest, Dec 15 1998
STATUS
approved

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Last modified April 14 04:54 EDT 2024. Contains 371655 sequences. (Running on oeis4.)