B Counting intersections of lines in a triangle

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The discussion revolves around the problem of counting intersections of lines drawn from the vertices of a triangle to points dividing the sides into equal segments. It establishes that the number of intersection points where three lines meet can be represented by the equation abc = (n-a)(n-b)(n-c), with specific solutions for even and odd values of n. The conversation also explores how to calculate the total number of regions formed by these lines, leading to a formula for the number of regions based on the number of lines drawn from each vertex. Additionally, the participants discuss the rarity of odd solutions and the patterns observed in even solutions, indicating a deeper mathematical exploration of the relationships between n, a, b, and c. The thread concludes with ongoing inquiries into the nature of solutions for various values of n, particularly focusing on prime factors.
  • #31
It generates a large number of solutions, but not all:
n= 35, a= 5 , b= 21 c= 28
As three numbers need a common divisor, we have m=7 as only option (m=1 doesn't fit with the generating equations). This leads to k=5 and c=1:
(7*5 ; 3*7 , 4*7 , 1*5)
We also need 7=1+2*3 (correct) and 1=(5-4)(5-3) (wrong).

k=a+b, k=a+a and k=b+b lead to the trivial solutions.

Code:
15	5	5	12
15	10	10	3
20	5	5	18
20	15	15	2
35	7	14	30
42	7	28	30
55	11	33	40
63	9	27	56
63	21	28	45
65	26	26	45
65	39	39	20
66	11	22	60
72	16	24	63
77	11	44	63
78	13	13	75
85	17	17	80
90	27	36	70
99	11	44	90
112	16	32	105
136	51	51	100
152	19	57	140
175	75	75	112
203	58	58	175
259	37	37	252
290	29	116	270
310	62	93	280
 

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