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14 | 14 | For the even integer $10$, we have three pairs: $(3,7), \; (5,5), \; (7,3)$ |
15 | 15 | and the minimal one is $(3,7)$ because |
16 | 16 | $3$ is the smallest among all $p_i$ values: $3, 5, 7$. |
17 | | - |
18 | | - |
19 | 17 | Consider the following minimal Goldbach pairs for even integer $2k$ within the range $6 \leq 2k \leq 50$ |
20 | 18 | \begin{align*} |
21 | | - 6 &= 3 + 3, & 30 &= 7 + 23, \\ |
22 | | - 8 &= 3 + 5, & 32 &= 3 + 29, \\ |
23 | | - 10 &= 3 + 7, & 34 &= 3 + 31, \\ |
24 | | - 12 &= 5 + 7, & 36 &= 5 + 31, \\ |
25 | | - 14 &= 3 + 11, & 38 &= 7 + 31, \\ |
26 | | - 16 &= 3 + 13, & 40 &= 3 + 37, \\ |
27 | | - 18 &= 5 + 13, & 42 &= 5 + 37, \\ |
28 | | - 20 &= 3 + 17, & 44 &= 3 + 41, \\ |
29 | | - 22 &= 3 + 19, & 46 &= 3 + 43, \\ |
30 | | - 24 &= 5 + 19, & 48 &= 5 + 43, \\ |
31 | | - 26 &= 3 + 23, & 50 &= 3 + 47, \\ |
32 | | - 28 &= 5 + 23, & |
| 19 | + 6 &= 3 + 3, & 24 &= 5 + 19, & 40 &= 3 + 37, \\ |
| 20 | + 8 &= 3 + 5, & 26 &= 3 + 23, & 42 &= 5 + 37, \\ |
| 21 | + 10 &= 3 + 7, & 28 &= 5 + 23, & 44 &= 3 + 41, \\ |
| 22 | + 12 &= 5 + 7, & 30 &= 7 + 23, & 46 &= 3 + 43, \\ |
| 23 | + 14 &= 3 + 11, & 32 &= 3 + 29, & 48 &= 5 + 43, \\ |
| 24 | + 16 &= 3 + 13, & 34 &= 3 + 31, & 50 &= 3 + 47, \\ |
| 25 | + 18 &= 5 + 13, & 36 &= 5 + 31, & \\ |
| 26 | + 20 &= 3 + 17, & 38 &= 7 + 31, & \\ |
| 27 | + 22 &= 3 + 19, & & |
33 | 28 | \end{align*} |
34 | 29 | We can notice that minimal Goldbach pairs with minimal $p_i=3$ produce a sequence of odd prime numbers |
35 | 30 | $p_j = 3, \; 5, \; 7, \; 11, \; 13, \; 17 \; \dots$ which is quite remarkable: |
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55 | 50 | Let $G_{\min} (2N)$ be a function that returns a set of minimal Goldbach pairs $(p_i, p_j)$ having $\min p_i$ |
56 | 51 | over the range $6 \leq 2k \leq 2N$ |
57 | 52 | \begin{align*} |
58 | | - G_{\min} (2N) = \{(p_i, p_j) \mid p_i + p_j = 2k \mid 6 \leq 2k \leq 2N \mid \min p_i \}. |
| 53 | + G_{\min} (2N) = \{(p_i, p_j) \mid p_i + p_j = 2k \mid 6 \leq 2k \leq 2N \mid \min p_i \} |
59 | 54 | \end{align*} |
60 | | - |
61 | 55 | For example, |
62 | 56 | \begin{align*} |
63 | 57 | G_{\min}(20) = \{ |
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94 | 88 | Hence, by excluding the elements of the set $W_{2N}(5)$ from the set $W_{2N}(3)$ yields the sequence of |
95 | 89 | lesser twin primes~\cite{oeis:A001359} |
96 | 90 | \begin{align*} |
97 | | - W_{2N}(3) \setminus W_{2N}(5) = \{ 3, \; 5, \; 11, \; 17, \; 29, \; 41, \; 59, \; 71, \; 101, \; 107, \; 137, \; \dots, \; p \leq 2N - 3 \} |
| 91 | + \mathtt{Lesser \; twin \; primes} &= \{ 3, \; 5, \; 11, \; 17, \; 29, \; 41, \; 59, \; 71, \; 101, \; 107, \; 137, \; \dots, \; p \leq 2N - 3 \} \\ |
| 92 | + &= W_{2N}(3) \setminus W_{2N}(5) |
98 | 93 | \end{align*} |
99 | | -This implies that the number of twin primes in range $6 \leq 2k \leq 2N$ can be expressed in terms of $F_{2N}(P)$ |
| 94 | +Above relation holds because the function $W_{2N}(5)$ generates the primes $p=6n+1$ such that either |
| 95 | +\begin{itemize} |
| 96 | + \item $p+2$ is composite: $p+2 = 3(2n+1)$ |
| 97 | + \item $p-2$ is composite or lesser twin prime |
| 98 | +\end{itemize} |
| 99 | +As a result, by excluding $W_{2N}(3) \setminus W_{2N}(5)$ we get the sequence of lesser twin primes. |
| 100 | +This implies that the number of twin primes $\pi_2$ in range $6 \leq 2k \leq 2N$ can be expressed in terms of $F_{2N}(P)$ |
100 | 101 | \begin{align*} |
101 | 102 | \pi_2 (2N) = F_{2N+3}(3) - F_{2N+5}(5) |
102 | 103 | \end{align*} |
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