

A100614


Numbers n such that (!n)/2 is prime, where !n = Sum_{k=0..n1} k!.


3



3, 4, 5, 8, 9, 10, 11, 30, 76, 163, 271, 273, 354, 721, 1796, 3733, 4769, 9316, 12221, 41532
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OFFSET

1,1


COMMENTS

No other terms below 50000.  Serge Batalov, Jul 23 2017


REFERENCES

R. K. Guy, Unsolved Problems In Number Theory, B44.


LINKS

Table of n, a(n) for n=1..20.
Yves Gallot, Is the number of primes (of half the left handed factorials) finite?.
Eric Weisstein's World of Mathematics, Left Factorial
Eric Weisstein's World of Mathematics, Integer Sequence Primes


FORMULA

When A014288(n1) is prime.


MATHEMATICA

s = 1; Do[s = s + n!; If[ PrimeQ[s/2], Print[n + 1]], {n, 10^3}] (* Robert G. Wilson v, Dec 02 2004 *)


CROSSREFS

Cf. A014288, Left factorials: A003422.
See A124375 for another version.
Sequence in context: A112594 A188003 A120519 * A274231 A173999 A127427
Adjacent sequences: A100611 A100612 A100613 * A100615 A100616 A100617


KEYWORD

nonn,more


AUTHOR

R. K. Guy, Dec 02 2004


EXTENSIONS

a(14) from Robert G. Wilson v, Dec 02 2004
a(15)=1796 from Ray Chandler, Dec 02 2004
a(17) from T. D. Noe, Dec 04 2004
Corrected by adding a(16)=3733 from Eric W. Weisstein, Oct 29 2005
a(18)=9316 from Eric W. Weisstein, Dec 27 2005
a(19)=12221 from Eric W. Weisstein, Oct 19 2006
a(20)=41532 from Serge Batalov, Jul 22 2017


STATUS

approved



