OFFSET
1,2
COMMENTS
Numbers n such that (620*10^n - 17)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime.
Numbers corresponding to terms <= 731 are certified primes.
a(16) > 10^5. - Robert Price, Sep 15 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103046(n+1) - 1.
EXAMPLE
67 is prime, hence 0 is a term.
MATHEMATICA
Select[Range[0, 300], PrimeQ[(620*10^# - 17)/9] &] (* Robert Price, Sep 15 2015 *)
PROG
(PARI) a=67; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+17)
(PARI) for(n=0, 1500, if(isprime((620*10^n-17)/9), print1(n, ", ")))
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004
EXTENSIONS
a(10)-a(12) from Kamada data by Ray Chandler, Apr 30 2015
a(13)-a(15) from Robert Price, Sep 15 2015
STATUS
approved