OFFSET
2,1
COMMENTS
Except the 1, all positive integers have nonmiddle divisors.
The nonmiddle divisors of n are here the divisors of n that are not in the half-open interval [sqrt(n/2), sqrt(n*2)).
LINKS
Amiram Eldar, Table of n, a(n) for n = 2..6375 (rows for n = 2..1000, flattened)
EXAMPLE
Triangle begins starting in row n = 2:
2;
1, 3;
1, 4;
1, 5;
1, 6;
1, 7;
1, 4, 8;
1, 9;
1, 2, 5, 10;
1, 11;
1, 2, 6, 12;
...
For n = 12 the divisors of 12 are [1, 2, 3, 4, 6, 12] and the middle divisors are [3, 4], so the nonmiddle divisors are [1, 2, 6, 12], the same as the row n = 12 of the triangle.
MATHEMATICA
row[n_] := Select[Divisors[n], !(Sqrt[n/2] <= # < Sqrt[2*n]) &]; Table[row[n], {n, 2, 28}] // Flatten (* Amiram Eldar, Jul 29 2024 *)
CROSSREFS
KEYWORD
AUTHOR
Omar E. Pol, Jul 28 2024
STATUS
approved