OFFSET
1,3
COMMENTS
Numbers n such that (580*10^n + 23)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 4 followed by digit 7 is prime.
Numbers corresponding to terms <= 886 are certified primes.
a(25) > 10^5. - Robert Price, Sep 15 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103036(n) - 1.
EXAMPLE
647 is prime, hence 1 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(580*10^# + 23)/9] &] (* Robert Price, Sep 15 2015 *)
PROG
(PARI) a=67; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-23)
(PARI) for(n=0, 1500, if(isprime((580*10^n+23)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(20)-a(23) from Kamada data by Ray Chandler, Apr 30 2015
a(24) from Robert Price, Sep 15 2015
STATUS
approved