OFFSET
1,1
COMMENTS
a(9) > 113500.
a(9) > 1000000, a(10) > 237000, a(11) > 209021. - Sean A. Irvine, Jan 10 2023
a(n)-1 is squarefree for all n. - Chai Wah Wu, Jan 30 2023
EXAMPLE
a(3) = 47 since 47^(2*3-1) - 1 = 229345006 = 2*11*23*31*14621 is the product of 5 distinct primes and 47 is the smallest prime number with this property.
PROG
(PARI) isok(p, n) = my(f=factor(p^(2*n-1)-1)); issquarefree(f) && (omega(f) == 2*n-1);
a(n) = my(p=2); while (!isok(p, n), p=nextprime(p+1)); p; \\ Michel Marcus, Dec 15 2022
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Kevin P. Thompson, Dec 15 2022
STATUS
approved