|
Problems & Puzzles:
Puzzles
Puzzle 1283 A
kind of flip side of Puzzle 1282
On September 25, 2026,
Tesfamichael B. Bogale sent the following puzzle:
Let p be a prime. Build a triangle of primes as
follows:
Row 1 contains just p. Row k (k =
2, 3, 4, ..., n) contains the next (2k - 1)
consecutive primes, carrying on from wherever the
previous row left off.
So the row sizes are
1, 3, 5, 7, 9, ..., n. After n rows, exactly n^2
primes have been used in total.
For each n
value, it is required that the sum of the primes in
each row, 2, 3, ...,n is a composite value (the
first row is always prime trivially). The triangle
ends when the sum of the primes in the row n+1 is a
prime.
Examples:
Example 1 (p = 2):
Row 1: 2 (sum = 2 prime,
trivial) Row 2: 3, 5, 7 (sum = 15
composite) Row 3: 11, 13, 17, 19, 23
(sum = 83 prime) So, p = 2 has one streak.
Example 2 (p = 11): Row
1: 11 (sum = 3 prime, trivial)
Row 2: 13, 17, 19 (sum = 49
composite) Row 3: 23, 29, 31, 37, 41
(sum = 161 composite) Row 4: 43, 47, 53, 59,
61, 67, 71 (sum = 401 prime) So, p = 11 has two
streaks.
Example 3 (p = 43): Row
1:
43 (sum = 3 prime, trivial) Row
2:
47, 53, 59 (sum = 159 composite) Row 3:
61, 67, 71, 73, 79 (sum = 351 composite)
Row 4:
83, 89, 97, 101, 103, 107, 109 (sum = 689 composite)
Row 4:
113, 127, 131, 137, 139, 149, 151, 157, 163
(sum = 1267 composite) Row 4: 167, 173, 179,
181, 191, 193, 197, 199, 211, 223, 227 (sum = 2141
prime) So, p = 43 has four streaks.
The
primes are picked based on the first smallest prime,
Sp, that breaks the record held by the previous
smallest prime. In the examples above, 11 breaks the
record held by 2, and 43 breaks the record held by
11. There is no prime between 2 and 11 that breaks
the record held by 2. Similarly, there is no prime
between 11 and 43 that breaks the record held by 11.
The process follows this trend.
I have found
the smallest p, Sp, for the first fourteen n values:
|
n |
Sp |
|
1 |
2 |
|
2 |
11 |
|
4 |
43 |
|
5 |
71 |
|
8 |
179 |
|
12 |
223 |
|
13 |
467 |
|
26 |
607 |
|
32 |
3,031 |
|
59 |
16,447 |
|
62 |
94,439 |
|
82 |
100,829 |
|
91 |
972,113 |
|
104 |
976,909 |
Q1. Can you
verify the values of the Table?
Q2. Can you
extend this Table, and find the next (n, Sp)?
|
|
|
|

|