OFFSET
1,1
COMMENTS
Thompson (2012) called these numbers "strictly 2-dense numbers" and proved that they are all phi-practical numbers (A260653).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Lola Thompson, Polynomials with divisors of every degree, Journal of Number Theory, Vol. 132, No. 5 (2012), pp. 1038-1053.
Lola Thompson, Variations on a question concerning the degrees of divisors of x^n - 1, Journal de Théorie des Nombres de Bordeaux, Vol. 26, No. 1 (2014), pp. 253-267.
MATHEMATICA
sdQ[n_] := SquareFreeQ[n] && Length[(d = Rest @ Most @ Divisors[n])] >0 && Max[Rest[d]/Most[d]] < 2; Select[Range[2, 15000, 2], sdQ]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Jul 23 2020
STATUS
approved