OFFSET
1,1
COMMENTS
Numbers n such that (830*10^n + 7)/9 is prime.
Numbers n such that digit 9 followed by n >= 0 occurrences of digit 2 followed by digit 3 is prime.
Numbers corresponding to terms <= 677 are certified primes.
a(12) > 10^5. - Robert Price, Oct 31 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103094(n) - 1.
EXAMPLE
922223 is prime, hence 4 is a term.
MATHEMATICA
Select[Range[0, 300], PrimeQ[(830*10^# + 7)/9] &] (* Robert Price, Oct 31 2015 *)
PROG
(PARI) a=93; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-7)
(PARI) for(n=0, 1500, if(isprime((830*10^n+7)/9 ), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more,less
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004
EXTENSIONS
One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(10) from Kamada data by Ray Chandler, Apr 28 2015
a(11) from Robert Price, Oct 31 2015
STATUS
approved