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A090704 Numbers n such that n*factorial(n)-1 is prime. 3

%I

%S 2,3,5,7,8,11,27,77,98,183,285,290,397,410,599,717,731,888,1962,2239,

%T 2241,2532,8799,11402

%N Numbers n such that n*factorial(n)-1 is prime.

%F a(n) = A049433(n)-1 because n!-(n-1)!-1 = (n-1)*(n-1)!-1.

%t Select[Range[2600],PrimeQ[#(#!)-1]&] (* Because a(22) generates a 7524 digit number to be tested for primality, the program takes a long time to run. *) (* _Harvey P. Dale_, May 27 2014 *)

%K nonn,more

%O 1,1

%A Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Jan 15 2004

%E More terms from _Farideh Firoozbakht_, Oct 31 2004

%E a(23)-a(24) using A049433 from _Michel Marcus_, May 29 2014

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Last modified September 22 21:04 EDT 2021. Contains 347608 sequences. (Running on oeis4.)