OFFSET
1,3
COMMENTS
Numbers n such that (750*10^n + 51)/9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 3 followed by digit 9 is prime.
Numbers corresponding to terms <= 847 are certified primes.
a(21) > 10^5. - Robert Price, Oct 20 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A103078(n) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
EXAMPLE
83339 is prime, hence 3 is a term.
MATHEMATICA
Flatten[Position[NestList[10#-51&, 89, 4200], _?PrimeQ]-1] (* Harvey P. Dale, Apr 05 2012 *)
Select[Range[0, 100000], PrimeQ[(750*10^# + 51)/9] &] (* Robert Price, Oct 20 2015 *)
PROG
(PARI) a=89; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-51)
(PARI) for(n=0, 1500, if(isprime((750*10^n+51)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 30 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(20) from Erik Branger May 01 2013 by Ray Chandler, Apr 29 2015
STATUS
approved