A124083 Numbers k such that prime(k)!/prime(k)# + 1 is prime.
1, 2, 3, 60, 90
Offset: 1
Examples
1*2/2 +1 = 2 prime so a(1)=1 as 2=prime(1). 1*2*3/(2*3) +1 = 2 prime so a(2)=2 as 3=prime(2). 1*2*3*4*5/(2*3*5) +1 = 5 prime so a(3)=3 as 5=prime(3).
Programs
-
PARI
isok(k) = isprime(prime(k)!/prod(i=1, k, prime(i)) + 1); \\ Michel Marcus, Sep 15 2019
Comments