OFFSET
1,3
COMMENTS
Numbers n such that (510*10^n + 21)/9 is prime.
Numbers n such that digit 5 followed by n >= 0 occurrences of digit 6 followed by digit 9 is prime.
Numbers corresponding to terms <= 937 are certified primes.
a(28) > 10^5. - Robert Price, Sep 05 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103018(n) - 1.
EXAMPLE
5669 is prime, hence 2 is a term.
MATHEMATICA
Flatten[Position[NestList[10#-21&, 59, 940], _?PrimeQ]]-1 (* Harvey P. Dale, Aug 22 2012 *)
PROG
(PARI) a=59; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-21)
(PARI) for(n=0, 1500, if(isprime((510*10^n+21)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004
EXTENSIONS
7 additional terms, corresponding to probable primes, from Ryan Propper, Jun 24 2005. Next term after 6811 is greater than 10,000.
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
Edited by T. D. Noe, Oct 30 2008
a(27) from Erik Branger May 01 2013 by Ray Chandler, Apr 30 2015
STATUS
approved