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A070089 P(n) < P(n+1) where P(n) (A006530) is the largest prime factor of n. 14

%I #17 Aug 02 2020 04:09:02

%S 1,2,4,6,8,9,10,12,16,18,20,21,22,24,25,27,28,30,32,33,36,40,42,45,46,

%T 48,50,52,54,56,57,58,60,64,66,68,70,72,75,77,78,81,82,84,85,88,90,91,

%U 92,93,96,98,100,102,105,106,108,110,112,114,115,117

%N P(n) < P(n+1) where P(n) (A006530) is the largest prime factor of n.

%C Erdős conjectured that this sequence has asymptotic density 1/2.

%C There are 500149 terms in this sequence up to 10^6, 4999951 up to 10^7, 49997566 up to 10^8, and 499992458 up to 10^9. With a binomial model with p = 1/2, these would be +0.3, -0.5, -0.0, and -0.5 standard deviations from their respective means. In other words, Erdős's conjecture seems solid. - _Charles R Greathouse IV_, Oct 27 2015

%C Erdős and Pomerance (1978) proved that the lower density of this sequence is at least 0.0099. This value was improved to 0.05544 (De La Bretèche et al., 2005), 0.1063 (Wang, 2017), 0.1356 (Wang, 2018), and 0.2017 (Lü and Wang, 2018). - _Amiram Eldar_, Aug 02 2020

%D H. L. Montgomery, Ten Lectures on the Interface Between Analytic Number Theory and Harmonic Analysis, Amer. Math. Soc., 1996, p. 210.

%H T. D. Noe, <a href="/A070089/b070089.txt">Table of n, a(n) for n = 1..1000</a>

%H Régis De La Bretèche, Carl Pomerance and Gérald Tenenbaum, <a href="https://doi.org/10.1007/s11139-005-0831-7">Products of ratios of consecutive integers</a>, The Ramanujan Journal, Vol. 9, No. 1-2 (2005), pp. 131-138, <a href="https://math.dartmouth.edu/~carlp/PDF/ABtemp.pdf">alternative link</a>.

%H Paul Erdős and Carl Pomerance, <a href="https://doi.org/10.1007/BF01818569">On the largest prime factors of n and n + 1</a>, Aequationes Math., Vol. 17, No. 1 (1978), pp. 311-321, <a href="http://www.math.dartmouth.edu/~carlp/PDF/paper17.pdf">alternative link</a>.

%H Xiaodong Lü and Zhiwei Wang, <a href="https://hal.archives-ouvertes.fr/hal-01797939/">On the largest prime factors of consecutive integers</a>, 2018.

%H Zhiwei Wang, <a href="https://doi.org/10.1090/proc/13459">On the largest prime factors of consecutive integers in short intervals</a>, Proceedings of the American Mathematical Society, Vol. 145, No. 8 (2017), pp. 3211-3220.

%H Zhiwei Wang, <a href="https://doi.org/10.1112/S0025579317000547">Sur les plus grands facteurs premiers d'entiers consécutifs</a>, Mathematika, Vol. 64, No. 2 (2018), pp. 343-379, <a href="https://arxiv.org/abs/1706.02980">preprint</a>, arXiv:1706.02980 [math.NT], 2017.

%t f[n_] := FactorInteger[n][[ -1, 1]]; Select[ Range[125], f[ # ] < f[ # + 1] &]

%o (PARI) gpf(n)=if(n<3,n,my(f=factor(n)[,1]); f[#f])

%o is(n)=gpf(n) < gpf(n+1) \\ _Charles R Greathouse IV_, Oct 27 2015

%Y Cf. A006530, A070087.

%K nonn

%O 1,2

%A _N. J. A. Sloane_, May 13 2002

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Last modified March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)