OFFSET
1,1
COMMENTS
Numbers n such that (380*10^n + 61)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 2 followed by digit 9 is prime.
Some of the larger entries may only correspond to probable primes.
Certified primality of number corresponding to term 2042 using Primo. - Ryan Propper, Jun 23 2005
a(5) > 10^5. - Robert Price, May 08 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A102987(n+1) - 1.
EXAMPLE
4229 is prime, hence 2 is a term.
MATHEMATICA
Select[Range[0, 3000], PrimeQ[(380*10^# + 61)/9] &] (* Robert Price, May 08 2015 *)
PROG
(PARI) a=49; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-61)
(PARI) for(n=0, 1500, if(isprime((380*10^n+61)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,bref,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007
a(4) from Kamada link by Ray Chandler, Apr 24 2015
STATUS
approved