A124249 - OEIS

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A124249

Numbers n such that n!! - 2^n is prime.

9, 13, 21, 25, 27, 35, 41, 53, 63, 81, 123, 333, 381, 413, 1187, 2265, 3153, 4211, 4887, 7359, 14161, 14643, 17299, 22107, 31487, 40235, 46711

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

All terms are odd.

a(28) > 50000. - Robert Price, Sep 04 2015

LINKS

Table of n, a(n) for n=1..27.

EXAMPLE

9 is in the sequence because 9!! - 2^9 = 433 is prime.

MATHEMATICA

Select[Range[0, 50000], #!! - 2^# > 0 && PrimeQ[#!! - 2^#] &] (* Robert Price, Sep 04 2015 *)

CROSSREFS

Cf. A124248.

Sequence in context: A026045 A371728 A304259 * A137168 A033870 A151901

Adjacent sequences: A124246 A124247 A124248 * A124250 A124251 A124252

KEYWORD

more,nonn

AUTHOR

Farideh Firoozbakht, Nov 27 2006

EXTENSIONS

Three more terms from Ryan Propper, Nov 05 2007

a(21)-a(27) from Robert Price, Sep 04 2015

STATUS

approved

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