login
This site is supported by donations to The OEIS Foundation.

 

Logo

Invitation: celebrating 50 years of OEIS, 250000 sequences, and Sloane's 75th, there will be a conference at DIMACS, Rutgers, Oct 9-10 2014.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A163209 Catalan pseudoprimes: odd composite integers n=2*m+1 satisfying A000108(m) == (-1)^m * 2 (mod n). 5
5907, 1194649, 12327121 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also, Wilson spoilers: composite n which divide A056040(n-1) - (-1)^floor(n/2). For the factorial function, a Wilson spoiler is a composite n that divides (n-1)! + (-1). Lagrange proved that no such n exists. For the swinging factorial (A056040), the situation is different.

Also, composite odd integers n=2*m+1 such that A000984(m) == (-1)^m (mod n).

Contains squares of A001220. In particular, a(2) = A001220(1)^2 = 1093^2 = 1194649 = A001567(274) and a(3) = A001220(2)^2 = 3511^2 = 12327121 = A001567(824).

See the Vardi reference for a binomial setup.

REFERENCES

Peter Luschny, "Divide, swing and conquer the factorial and the lcm{1,2,...,n}", preprint, April 2008.

I. Vardi, Computational Recreations in Mathematica, 1991, p.66.

LINKS

Table of n, a(n) for n=1..3.

C. Aebi, G. Cairns (2008). "Catalan numbers, primes and twin primes". Elemente der Mathematik 63 (4): 153-164. doi:10.4171/EM/103

Peter Luschny, Swinging Primes.

MAPLE

swing := proc(n) option remember; if n = 0 then 1 elif irem(n, 2) = 1 then swing(n-1)*n else 4*swing(n-1)/n fi end:

WS := proc(f, r, n) select(p->(f(p-1)+r(p)) mod p = 0, [$2..n]);

select(q -> not isprime(q), %) end:

A163209 := n -> WS(swing, p->(-1)^iquo(p+2, 2), n);

CROSSREFS

Sequence in context: A025513 A015295 A209431 * A216942 A031665 A031575

Adjacent sequences:  A163206 A163207 A163208 * A163210 A163211 A163212

KEYWORD

nonn,hard,more,bref

AUTHOR

Peter Luschny, Jul 24 2009

EXTENSIONS

a(1) = 5907 = 3*11*179 was found by S. Skiena

Typo corrected Peter Luschny, Jul 25 2009

Edited by Max Alekseyev, Jun 22 2012

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified October 1 10:32 EDT 2014. Contains 247508 sequences.