115743domain: NAppears in sequencesLeast k such that k*30^n-1 , k*30^n+1, and 2*k*30^n-1 are prime; that is, twin primes and a Sophie Germain prime.at n=38A212956a(n) is the index where n appears for first time in the list of first differences of the numbers with middle divisors.at n=26A390114