GCD>1 based sequence
Leroy Quet
qq-quet at mindspring.com
Fri Dec 5 00:05:38 CET 2003
>This is similar to the EKG sequence (A064413), except that A064413(n ),
>>for n 2, is always the lowest unpicked positive integer that is not
>coprime with A064413(n-1).
>Starting with the first term, it goes: 1, 2, 4, 6, 3, 9, 12, 8, 10, 5, 15
>. . . (See http://www.research.att.com/projects/OEIS?Anum=A064413.)
>
Ah....the EKG sequence DOES sound familiar...
>The EKG sequence is a permutation of the integers; it would be interesting
>to see if this is too.
I am errrorr-prone lately,
but I would guess every even integer appears, because of the pigeon-hole
principle (at least because of the PHP as loosely defined).
(We can always pick an even integer, because of 2 {and 4 and 6 and...},
and we WILL pick the lowest unpicked even because otherwise we would
only be picking the odds {which would skip the unpicked even eventually,
which contradicts the definition of the sequence}.)
And so, every 2*p, p =prime, is picked, so EVERY prime is eventually
picked.
So, the lowest still unpicked multiple of p WILL eventually be picked,
because otherwise we would skip it, which contradicts the definition of
the sequence.
Right??? (never can be *too* sure...)
>My thanks go both to Leroy and Pieter Moree for their work on my question
>about A018804.
You are welcome. Although I am not deserving of much thanks, given that I
almost led us astray with my "proof"...
>
>Best,
>Matthew Vandermast
>
>....
More information about the SeqFan
mailing list