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Date: 19-10-2019
698
Date: 12-10-2020
867
Date: 26-9-2020
559
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A Thâbit ibn Kurrah number, sometimes called a 321-number, is a number of the form . The first few for , 1, ... are 2, 5, 11, 23, 47, 95, 191, 383, 767, ... (OEIS A055010).
Note that there exist infinitely many odd integers such that is composite for every , and numbers with this property are called Riesel numbers.
REFERENCES:
Riesel, H. "Lucasian Criteria for the Primality of ." Math. Comput. 23, 869-875, 1969.
Sloane, N. J. A. Sequence and A055010 in "The On-Line Encyclopedia of Integer Sequences."
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