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 A118744 Primes of the form n!! + n - 1. 0

%I

%S 3,5,11,19,53,953,46091,34459441,3715891219,6332659870762850657,

%T 107145471557284795514880041

%N Primes of the form n!! + n - 1.

%C No additional terms up to n=2000. - _Harvey P. Dale_, Jul 27 2017

%D G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 159.

%e For n=2, 2!! + 2 - 1 = 2 + 2 - 1 = 3, which is prime;

%e for n=4, 4!! + 4 - 1 = 4*2 + 4 - 1 = 11, which is prime.

%p SFACT:= proc(n) local i,j,k; for k from 1 by 1 to n do i:=k; j:=k-2; while j >0 do i:=i*j; j:=j-2; od: if isprime(i+k-1) then print(i+k-1); fi; od: end: SFACT(550);

%t Select[Table[n!!+n-1,{n,100}],PrimeQ] (* _Harvey P. Dale_, Jul 27 2017 *)

%K nonn

%O 1,1

%A _Paolo P. Lava_ and _Giorgio Balzarotti_, May 22 2006

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Last modified August 12 16:40 EDT 2020. Contains 336439 sequences. (Running on oeis4.)