OFFSET
1,2
COMMENTS
Numbers n such that (670*10^n + 41)/9 is prime.
Numbers n such that digit 7 followed by n >= 0 occurrences of digit 4 followed by digit 9 is prime.
Numbers corresponding to terms <= 771 are certified primes.
a(14) > 10^5. - Robert Price, Sep 27 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103059(n) - 1.
EXAMPLE
74449 is prime, hence 3 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(670*10^# + 41)/9] &] (* Robert Price, Sep 27 2015 *)
PROG
(PARI) a=79; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-41)
(PARI) for(n=0, 1000, if(isprime((670*10^n+41)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(10)-a(12) from Kamada data by Ray Chandler, Apr 30 2015
a(13) from Robert Price, Sep 27 2015
STATUS
approved