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A123910 Numbers k such that k!!-4 is prime. 51
5, 7, 9, 11, 13, 15, 19, 25, 35, 79, 81, 105, 171, 243, 271, 295, 355, 523, 591, 1211, 3073, 11157, 12887, 19825 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Corresponding primes of the form k!!-4 = a(n)!!-4 are {11, 101, 941, 10391, 135131, 2027021, 654729071, 7905853580621, 221643095476699771871, ...}.

a(25) > 50000. - Robert Price, May 08 2015

LINKS

Table of n, a(n) for n=1..24.

Joe McLean, Interesting Sources of Probable Primes

MATHEMATICA

Do[f=n!!-4; If[PrimeQ[f], Print[{n, f}]], {n, 1, 355}]

CROSSREFS

Cf. A007749, A094144.

Sequence in context: A108144 A241835 A279914 * A024886 A083249 A077153

Adjacent sequences:  A123907 A123908 A123909 * A123911 A123912 A123913

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk, Oct 28 2006

EXTENSIONS

More terms from Farideh Firoozbakht, Nov 19 2006

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008

a(23)-a(24) from Robert Price, May 08 2015

STATUS

approved

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Last modified November 30 19:02 EST 2021. Contains 349424 sequences. (Running on oeis4.)