OFFSET
1,3
COMMENTS
Numbers n such that (580*10^n - 31)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 4 followed by digit 1 is prime.
Numbers corresponding to terms <= 612 are certified primes.
a(14) > 10^5. - Robert Price, Sep 10 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103034(n+1) - 1.
EXAMPLE
641 is prime, hence 1 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(580*10^# - 31)/9] &] (* Robert Price, Sep 10 2015 *)
PROG
(PARI) a=61; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+31)
(PARI) for(n=0, 1500, if(isprime((580*10^n-31)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004
EXTENSIONS
Two more terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 22 2007
a(13) from Max Alekseyev, Dec 12 2011
STATUS
approved