OFFSET
1,2
COMMENTS
Numbers n such that (490*10^n + 23)/9 is prime.
Numbers n such that digit 5 followed by n >= 0 occurrences of digit 4 followed by digit 7 is prime.
a(19) > 10^5. - Robert Price, Jul 29 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103015(n) - 1.
EXAMPLE
547 is prime, hence 1 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(490*10^# + 23)/9] &] (* Robert Price, Jul 29 2015 *)
PROG
(PARI) a=57; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-23)
(PARI) for(n=0, 1000, if(isprime((490*10^n+23)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004
EXTENSIONS
Three additional terms, corresponding to probable primes, from Ryan Propper, Jun 18 2005
5764 from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007
Edited by T. D. Noe, Oct 30 2008
a(16)-a(18) by Ray Chandler, Apr 24 2015
STATUS
approved