OFFSET
1,2
COMMENTS
Numbers n such that (520*10^n - 43)/9 is prime.
Numbers n such that digit 5 followed by n >= 0 occurrences of digit 7 followed by digit 3 is prime.
Numbers corresponding to terms <= 108 are certified primes.
a(15) > 10^5. - Robert Price, Sep 09 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103020(n) - 1.
EXAMPLE
57773 is prime, hence 3 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(520*10^# - 43)/9] &] (* Robert Price, Sep 09 2015 *)
PROG
(PARI) a=53; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+43)
(PARI) for(n=0, 1000, if(isprime((520*10^n-43)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004
EXTENSIONS
Five additional terms, corresponding to probable primes, from Ryan Propper, Jun 22 2005
Edited by T. D. Noe, Oct 30 2008
a(13)-a(14) from Kamada data by Ray Chandler, Apr 30 2015
STATUS
approved