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 A124083 Numbers k such that prime(k)!/prime(k)# + 1 is prime. 1

%I

%S 1,2,3,60,90

%N Numbers k such that prime(k)!/prime(k)# + 1 is prime.

%C a(6) > 500 if it exists. - _Felix FrÃ¶hlich_, Sep 15 2019

%e 1*2/2 +1 = 2 prime so a(1)=1 as 2=prime(1).

%e 1*2*3/(2*3) +1 = 2 prime so a(2)=2 as 3=prime(2).

%e 1*2*3*4*5/(2*3*5) +1 = 5 prime so a(3)=3 as 5=prime(3).

%o (PARI) isok(k) = isprime(prime(k)!/prod(i=1, k, prime(i)) + 1); \\ _Michel Marcus_, Sep 15 2019

%Y Cf. A092435 (p!/p#), A124082.

%K nonn,more

%O 1,2

%A _Pierre CAMI_, Nov 25 2006

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Last modified June 15 08:14 EDT 2021. Contains 345048 sequences. (Running on oeis4.)