OFFSET
1,2
COMMENTS
Numbers n such that (820*10^n + 71)/9 is a prime.
Numbers n such that digit 9 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime.
Numbers corresponding to terms <= 1139 are certified primes. For number corresponding to 10393 and larger see P. De Geest, PDP Reference Table.
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
Patrick De Geest, PDP Reference Table - 919.
Makoto Kamada, Prime numbers of the form 911...119.
FORMULA
a(n) = A082717(n) - 2.
EXAMPLE
919 is prime, hence 1 is a term.
MATHEMATICA
Flatten[Position[NestList[10#-71&, 99, 1200], _?PrimeQ]]-1 (* Harvey P. Dale, May 02 2012 *)
PROG
(PARI) a=99; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-71)
(PARI) for(n=0, 1500, if(isprime((820*10^n+71)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Robert G. Wilson v, Aug 18 2000
EXTENSIONS
Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004
Edited by N. J. A. Sloane, Jun 15 2007
One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
Edited comments section by Patrick De Geest, Nov 02 2014
Edited by Ray Chandler, Nov 04 2014
STATUS
approved