OFFSET
1,1
FORMULA
EXAMPLE
a(13) = -1 + (2*3*5*7*...*41)*k(13) = 304250263527210*74 and {22514519501013539, 22514519501013542} are the corresponding primes; k(13)=74 is the smallest suitable multiplier. Twin primes obtained from primorial numbers with k=1 multiplier seem to be much rarer (see A057706).
PROG
(PARI) a(n) = {my(q = prod(k=1, n, prime(k))); for(k=1, oo, if (isprime(q*k-1) && isprime(q*k+1), return(q*k-1)); ); } \\ Michel Marcus, Jul 10 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Mar 22 2001
EXTENSIONS
a(2)=5 corrected by Ray Chandler, Apr 03 2009
STATUS
approved