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 A100614 Numbers n such that (!n)/2 is prime, where !n = Sum_{k=0..n-1} k!. 2
 3, 4, 5, 8, 9, 10, 11, 30, 76, 163, 271, 273, 354, 721, 1796, 3733, 4769, 9316, 12221, 41532 (list; graph; refs; listen; history; text; internal format)
 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 Eric Weisstein's World of Mathematics, Left Factorial Eric Weisstein's World of Mathematics, Integer Sequence Primes FORMULA When A014288(n-1) 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

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Last modified January 17 20:36 EST 2020. Contains 330987 sequences. (Running on oeis4.)