The PF factorization of 2156 is: 2 x 2 x 7 x 7 x 11
2156
1078,2
539,2,2
77,7,2,2
11,7,7,2,2
1997 is already prime; no tree.
51 3,17
350=2x5x5x7
33 11,3
a prime factorization tree
50 25,2 5,5,2
97 is already prime; no tree.
131 is already prime. No tree.
141 = 3 x 47
572=2x286=2x2x143=2x2x11x13
585 195,3 65,3,3 13,5,3,3
3 is already prime. No need for a tree.