|
|
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 b-file.
All the numbers end in 9.
|
|
REFERENCES
|
G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 159.
|
|
LINKS
|
|
|
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
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|