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A093437 a(n) = largest prime of the form n!/k! + 1. 3
2, 2, 3, 7, 13, 61, 31, 2521, 20161, 15121, 604801, 39916801, 3991681, 3113510401, 14529715201, 54486432001, 10461394944001, 59281238016001, 53353114214401, 2, 670442572801, 8515157028618240001, 9366672731480064001 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Is 19 the largest n such that a(n) = 2?  There are none for 19 < n <= 600. - Robert Israel, Jan 16 2017

LINKS

Robert Israel, Table of n, a(n) for n = 0..466

EXAMPLE

a(7) = 2521 because 7!/2! + 1 = 2521 is prime, whereas 7!/1! + 1 = 5041 = 71^2 is composite;

a(19) = 2 because the only prime of the form 19!/k! + 1 is 19!/19! + 1 = 2.

MAPLE

f:= proc(n) local k, x;

  x:= n!;

  for k from 2 do

    if isprime(x+1) then return x+1 fi;

    x:= x/k;

  od

end proc:

map(f, [$0..40]); # Robert Israel, Jan 16 2017

CROSSREFS

Cf. A093621 (smallest k > 0 such that n!/k! + 1 is prime), A002981 (n! + 1 is prime), A088332 (primes of form n! + 1).

Sequence in context: A068524 A184841 A109277 * A075059 A060357 A064714

Adjacent sequences:  A093434 A093435 A093436 * A093438 A093439 A093440

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Apr 01 2004

EXTENSIONS

Corrected and extended by Hugo Pfoertner, Apr 06 2004

STATUS

approved

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Last modified April 14 10:14 EDT 2021. Contains 342949 sequences. (Running on oeis4.)