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Search: id:A100614
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| A100614 |
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Numbers n such that (!n)/2 is prime, where !n = sum_{k=0..n-1} k!. |
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+0
2
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| 3, 4, 5, 8, 9, 10, 11, 30, 76, 163, 271, 273, 354, 721, 1796, 3733, 4769, 9316, 12221
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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R. K. Guy, Unsolved Problems In Number Theory, B44.
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LINKS
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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
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FORMULA
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When A014288(n-1) is prime.
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MATHEMATICA
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s = 1; Do[s = s + n!; If[ PrimeQ[s/2], Print[n + 1]], {n, 10^3}] (from Robert G. Wilson v Dec 02 2004)
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CROSSREFS
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Cf. A014288, Left factorials: A003422.
See A124375 for another version.
Sequence in context: A105020 A112594 A120519 this_sequence A127427 A047205 A120631
Adjacent sequences: A100611 A100612 A100613 this_sequence A100615 A100616 A100617
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KEYWORD
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nonn
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AUTHOR
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R. K. Guy (rkg(AT)cpsc.ucalgary.ca), Dec 02 2004
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EXTENSIONS
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a(14) from Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 02 2004
a(15)=1796 from Ray Chandler (rayjchandler(AT)sbcglobal.net), Dec 02 2004
a(17) from T. D. Noe (noe(AT)sspectra.com), Dec 04 2004
Corrected by adding a(16)=3733 from Eric Weisstein (eric(AT)weisstein.com), Oct 29 2005
a(18)=9316 from Eric Weisstein (eric(AT)weisstein.com), Dec 27, 2005
a(19)=12221 from Eric Weisstein (eric(AT)weisstein.com), Oct 19, 2006
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