OFFSET
1,2
COMMENTS
Numbers n such that (890*10^n - 17)/9 is prime.
Numbers n such that digit 9 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime.
Numbers corresponding to terms <= 528 are certified primes.
a(22) > 10^5. - Robert Price, Nov 14 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103109(n) - 1.
EXAMPLE
9888887 is prime, hence 5 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(890*10^# - 17)/9] &] (* Robert Price, Nov 14 2015 *)
PROG
(PARI) a=97; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+17)
(PARI) for(n=0, 1000, if(isprime((890*10^n-17)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(15)-a(19) from Kamada data by Ray Chandler, Apr 29 2015
a(20)-a(21) from Robert Price, Nov 14 2015
STATUS
approved