OFFSET
1,2
COMMENTS
Numbers n such that (560*10^n + 43)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 2 followed by digit 7 is prime.
Numbers corresponding to terms <= 126 are certified primes.
a(5) > 10^5. - Robert Price, Sep 12 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A097402(n+1) - 1.
EXAMPLE
67 is prime, hence 0 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(560 * 10^# + 43)/9] &] (* Robert Price, Sep 12 2015 *)
PROG
(PARI) a=67; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-43)
(PARI) for(n=0, 1000, if(isprime((560*10^n+43)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004
STATUS
approved