OFFSET
1,1
COMMENTS
Numbers k such that P(k)^2 | k and P(k+1)^2 | (k+1), where P(k) = A006530(k).
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..12072 (all terms <= 10^11)
Jean-Marie De Koninck, Nicolas Doyon, and Florian Luca, Consecutive integers divisible by the square of their largest prime factors, Journal of Combinatorics and Number Theory, Vol. 5, No. 2 (2013), pp. 81-93; Researchgate link.
Jean-Marie De Koninck and Matthieu Moineau, Consecutive Integers Divisible by a Power of their Largest Prime Factor, J. Integer Seq., Vol. 21 (2018), Article 18.9.3.
Régis de la Bretèche and Sary Drappeau, Niveau de répartition des polynômes quadratiques et crible majorant pour les entiers friables, Journal of the European Mathematical Society, Vol. 22, No. 5 (2020), pp. 1577-1624; arXiv preprint, arXiv:1703.03197 [math.NT], 2017-2019.
Daniel Suteu, Table of n, a(n) for n = 1..112589 (all terms <= 10^13)
FORMULA
x^(1/4)/log(x) << N(x) << x*exp(-c*sqrt(2*log(x)*log(log(x)))), where N(x) is the number of terms <= x, c = 25/24 (De Koninck et al., 2013), or 4/sqrt(5) (de la Bretèche and Drappeau, 2020).
EXAMPLE
8 = 2^3 is a term since P(8) = 2 and 2^2 | 8, 9 = 3^2, P(9) = 3 and 3^2 | 9.
675 = 3^3 * 5^2 is a term since P(675) = 5, 5^2 | 675, 676 = 2^2 * 13^2, P(676) = 13 and 13^2 | 676.
MATHEMATICA
q[n_] := FactorInteger[n][[-1, 2]] > 1; Select[Range[250000], q[#] && q[# + 1] &]
PROG
(Python)
from sympy import factorint
def c(n): f = factorint(n); return f[max(f)] >= 2
def ok(n): return n > 1 and c(n) and c(n+1)
print(list(filter(ok, range(235225)))) # Michael S. Branicky, May 30 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, May 30 2022
STATUS
approved