OFFSET
1,4
COMMENTS
p(k) is k-th prime; p(n)# is n-th primorial, A002110(n). For the larger n, these are only counts of highly probable primes. Of the first 500 terms, the maximum occurs twice, a(366)=a(432)=7; the mode is 2, occurring 142 times.
LINKS
Rick Shepherd, Table of n, a(n) for n = 1..500
EXAMPLE
a(6)=4 because p(6)#=A002110(6)=30030 and 30030/3-1=10009, 30030/7-1=4289, 30030/11-1=2729 and 30030/13-1=2309 are all prime and there are no other primes of this form.
PROG
(PARI) a(n)= p=prod(k=1, n, prime(k)); sum(k=1, n, isprime(p/prime(k)-1))
CROSSREFS
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Nov 28 2007
STATUS
approved