Even Integers not Expressible as Sum of 3, 5 or 7 with Prime

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Theorem

The even integers that cannot be expressed as the sum of $2$ prime numbers where one of those primes is $3$, $5$ or $7$ begins:

$98, 122, 124, 126, 128, 148, 150, \ldots$

This sequence is A283555 in the On-Line Encyclopedia of Integer Sequences (N. J. A. Sloane (Ed.), 2008).


Proof

These are the primes which coincide with the upper end of a prime gap greater than $6$.

These can be found at:

$89$ to $97$: prime gap of $8$
$113$ to $127$: prime gap of $14$
$139$ to $149$: prime gap of $10$

and so on.


We have that:

\(\ds 98\) \(=\) \(\ds 19 + 79\)
\(\ds 122\) \(=\) \(\ds 13 + 109\)
\(\ds 124\) \(=\) \(\ds 11 + 113\)
\(\ds 126\) \(=\) \(\ds 13 + 113\)
\(\ds 128\) \(=\) \(\ds 19 + 109\)

and so on.

$\blacksquare$


Sources