

A118813


Primes of the form (2n)!  n!  1.


2




OFFSET

1,1


COMMENTS

The term a(7) (2407 digits) is too large to include even in the bfile.
All the numbers end in 9.
For all n, (2n)!  n!  1 has exactly A027868(n) trailing 9s.  Rick L. Shepherd, Feb 16 2014
Generated by n = 5, 7, 8, 15, 103, 179, ....  R. J. Mathar, Sep 20 2012 (now A238011)


REFERENCES

G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 159.


LINKS

Rick L. Shepherd, Table of n, a(n) for n = 1..6


EXAMPLE

For n=5, (2*5)!  5!  1 = 3628800  120  1 = 3628679, which is prime.


MAPLE

PFACT:=proc(N) local i, r; for i from 1 by 1 to N do r:=(2*i)!i!1; if isprime(r) then print(i); fi; od; end: PFACT(100);


CROSSREFS

Cf. A238011 (corresponding n), A118812, A237443.
Sequence in context: A252499 A235970 A116221 * A127229 A269128 A068158
Adjacent sequences: A118810 A118811 A118812 * A118814 A118815 A118816


KEYWORD

nonn


AUTHOR

Paolo P. Lava and Giorgio Balzarotti, May 23 2006


STATUS

approved



