[seqfan] Re: A178375

Max Alekseyev maxale at gmail.com
Wed May 26 20:21:59 CEST 2010

On Wed, May 26, 2010 at 10:53 AM, Vladimir Shevelev <shevelev at bgu.ac.il> wrote:

> %N A178375 Let c(n)=gcd(A000032(n)-1,A001608(n)). Then a(n)=1, if c(n)=1; otherwise, a(n) is the maximal prime divisor of c(n) [A000032=Lucas sequence; A001608=Perrin sequence]
> %C A178375 If n is prime, then n divides c(n). We call n a Lucas-Perrin pseudoprime if n is composite and divides c(n).

> Can anyone  find a few "Lucas-Perrin pseudoprimes" ? (the drfinition see in %C)

They form the intersection of A005845 and A013998.
Only one of currently listed terms of A013998 belongs to A005845 -
it's 46672291.
Yet another pseudoprime comes from A018187 (a subsequence of A013998)
- it's 7045248121.
Perhaps, the sequence of Lucas-Perrin pseudoprimes starts with:
46672291, 7045248121, ...


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