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A118813

Primes of the form (2*k)! - k! - 1.

3628679, 87178286159, 20922789847679, 265252859812191058635000805631999

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.

For all k, (2*k)! - k! - 1 has exactly A027868(k) trailing 9s. - Rick L. Shepherd, Feb 16 2014

Generated by k = 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

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.

KEYWORD

nonn

AUTHOR

STATUS

approved

URL: https://oeis.org/A118813