# Interval containing Prime Number of forms 4n - 1, 4n + 1, 6n - 1, 6n + 1

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## Theorem

Let $n \in \Z$ be an integer such that $n \ge 118$.

Then between $n$ and $\dfrac {4 n} 3$ there exists at least one prime number of each of the forms:

- $4 m - 1, 4 m + 1, 6 m - 1, 6 m + 1$

## Proof

It is demonstrated that the result is true for $n = 118$:

- $\dfrac {4 \times 118} 3 = 157 \cdotp \dot 3$

The primes between $118$ and $157$ are:

\(\ds 127\) | \(=\) | \(\ds 4 \times 32 - 1\) | ||||||||||||

\(\ds \) | \(=\) | \(\ds 6 \times 21 + 1\) | ||||||||||||

\(\ds 131\) | \(=\) | \(\ds 4 \times 33 - 1\) | ||||||||||||

\(\ds \) | \(=\) | \(\ds 6 \times 22 - 1\) | ||||||||||||

\(\ds 137\) | \(=\) | \(\ds 4 \times 34 + 1\) | ||||||||||||

\(\ds \) | \(=\) | \(\ds 6 \times 23 - 1\) | ||||||||||||

\(\ds 139\) | \(=\) | \(\ds 4 \times 35 - 1\) | ||||||||||||

\(\ds \) | \(=\) | \(\ds 6 \times 23 + 1\) | ||||||||||||

\(\ds 149\) | \(=\) | \(\ds 4 \times 37 + 1\) | ||||||||||||

\(\ds \) | \(=\) | \(\ds 6 \times 25 - 1\) | ||||||||||||

\(\ds 151\) | \(=\) | \(\ds 4 \times 38 - 1\) | ||||||||||||

\(\ds \) | \(=\) | \(\ds 6 \times 25 + 1\) | ||||||||||||

\(\ds 157\) | \(=\) | \(\ds 4 \times 39 + 1\) | ||||||||||||

\(\ds \) | \(=\) | \(\ds 6 \times 26 + 1\) |

So it can be seen that:

- the primes of the form $4 m - 1$ are:
- $127, 131, 139, 151$

- the primes of the form $4 m + 1$ are:
- $137, 139, 157$

- the primes of the form $6 m - 1$ are:
- $131, 137, 149$

- the primes of the form $6 m + 1$ are:
- $127, 139, 151, 157$

and so the conditions of the result are fulfilled for $118$.

But then note we have:

- $\dfrac {4 \times 117} 3 = 156$

and so the primes between $117$ and $157$ are the same ones as between $118$ and $157$, excluding $157$ itself.

Thus the conditions also hold for $117$.

It is puzzling as to why the condition $n \ge 118$ has been applied to the initial statement.

## Sources

- 1986: David Wells:
*Curious and Interesting Numbers*... (previous) ... (next): $118$ - 1997: David Wells:
*Curious and Interesting Numbers*(2nd ed.) ... (previous) ... (next): $118$