OFFSET
1,2
COMMENTS
Numbers n such that 70*10^n + 3 is prime.
Numbers n such that digit 7 followed by n >= 0 occurrences of digit 0 followed by digit 3 is prime.
Numbers corresponding to terms <= 239 are certified primes.
Certified primality of number corresponding to term 1047 with Primo. - Ryan Propper, Jun 20 2005
a(23) > 2*10^5. - Robert Price, Aug 15 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A097970(n) - 1.
EXAMPLE
7000003 is prime, hence 5 is a term.
MATHEMATICA
Select[Range[0, 200000], PrimeQ[70*10^# + 3] &] (* Robert Price, Aug 15 2015 *)
PROG
(PARI) a=73; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-27)
(PARI) for(n=0, 1500, if(isprime(70*10^n+3), print1(n, ", ")))
(Magma) [n: n in [0..500] | IsPrime(70*10^n + 3)]; // Vincenzo Librandi, Aug 16 2015
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(14)-a(19) from Kamada data by Ray Chandler, Apr 29 2015
a(20)-a(22) from Robert Price, Aug 15 2015
STATUS
approved