Arises from generalized Lucas-Lehmer test for primality.

[Davide Rotondo]

A018844
Arises from generalized Lucas-Lehmer test for primality.
4, 10, 52, 724, 970, 10084, 95050, 140452, 1956244, 9313930, 27246964, 379501252, 912670090, 5285770564, 73621286644, 89432354890, 1025412242452, 8763458109130, 14282150107684, 198924689265124,...

I observed that these values are congruent to 3 or 4 mod 7.

What do you think?

See you soon

Davide

[Gareth McCaughan]

Description says "m belongs to the sequence iff m-2 is twice a square and m+2 is either three or six times a square".

The squares mod 7 are 0, 1, 2, 4.

So 2*square+2 means 2,4,6,3, so the first condition requires m to be 2,3,4,6 mod 7.

3*square-2 means 5,1,4,3 and 6*square-2 means 0,4,3,1, so the second condition requires m to be 0,1,3,4,5 mod 7.

So the two conditions together require m to be 3 or 4 mod 7.

(There will be similar things to say modulo other primes.)

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