OFFSET
1,2
COMMENTS
If n has d divisors, n has an infinite number of multiples with exactly 2d divisors, but only a finite number of multiples with fewer than 2d divisors.
Conjecture: row n includes n^2 if and only if n is a power of a prime number (A000961).
EXAMPLE
Triangle begins:
1;
2, 4;
3, 9;
4, 8, 16;
5, 25;
6, 12, 18;
7, 49;
8, 16, 32, 64;
9, 27, 81;
10, 20, 50;
11, 121;
12, 24, 36, 48;
13, 169;
14, 28, 98;
15, 45, 75;
16, 32, 64, 128, 256;
...
PROG
(PARI) row(n) = select(x->((numdiv(x)<2*numdiv(n)) && !(x % n)), [1..n^2]); \\ Michel Marcus, Jan 26 2021
CROSSREFS
KEYWORD
nonn,tabf
AUTHOR
J. Lowell, Jan 25 2021
STATUS
approved