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A093437
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a(n) = largest prime of the form n!/k! + 1.
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3
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2, 2, 3, 7, 13, 61, 31, 2521, 20161, 15121, 604801, 39916801, 3991681, 3113510401, 14529715201, 54486432001, 10461394944001, 59281238016001, 53353114214401, 2, 670442572801, 8515157028618240001, 9366672731480064001
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OFFSET
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0,1
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COMMENTS
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Is 19 the largest n such that a(n) = 2? There are none for 19 < n <= 600. - Robert Israel, Jan 16 2017
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LINKS
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Robert Israel, Table of n, a(n) for n = 0..466
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EXAMPLE
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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.
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MAPLE
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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
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CROSSREFS
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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
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy, Apr 01 2004
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EXTENSIONS
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Corrected and extended by Hugo Pfoertner, Apr 06 2004
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STATUS
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approved
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