Journal of Integer Sequences, Vol. 20 (2017), Article 17.3.2

A Tribonacci-Like Sequence of Composite Numbers


Ivan Lunev
Department of Mathematics and Mechanics
Saint-Petersburg State University
28 Universitetsky Prospect
St. Petersburg, 198504
Russia

Abstract:

We find a new Tribonacci-like sequence of positive integers ⟨ x0, x1, x2, ... ⟩ given by xn = xn-1 + xn-2 + xn-3, n ≥ 3, and gcd(x0,x1,x2) = 1 that contains no prime numbers. We show that the sequence with initial values x0 = 151646890045, x1 = 836564809606, x2 = 942785024683 is the current record in terms of the number of digits.


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(Concerned with sequences A000045 A000073 A056993.)


Received November 20 2016; revised versions received November 25 2016; December 27 2016; January 3 2017. Published in Journal of Integer Sequences, January 3 2017.


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