a(1)= because 3*10^11 = 29 and 3*10^1+1 = 31 are primes.
a(2)= because 6*10^11 = 59 and 6*10^1+1 = 61 are primes.
a(3)= because 6*10^21 = 599 and 6*10^2+1 = 601 are primes.
a(4)= because 3*10^31 = 2999 and 3*10^3+1 = 3001 are primes.
a(5)= because 9*10^31 = 8999 and 9*10^3+1 = 9001 are primes.
a(6)= because 3*10^71 = 29999999 and 3*10^7+1 = 30000001 are primes.
