OFFSET
1,1
COMMENTS
Numbers n such that (290*10^n + 7)/9 is prime.
Numbers n such that the digit 3 followed by n >= 0 occurrences of the digit 2 followed by the digit 3 is prime.
Numbers corresponding to terms <= 3035 are certified primes.
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
Patrick De Geest, PDP Reference Table - 323.
Makoto Kamada, Prime numbers of the form 322...223.
FORMULA
a(n) = A082705(n) - 2.
EXAMPLE
3222223 is prime, hence 5 is a term.
MATHEMATICA
Select[Range[0, 2000], PrimeQ[(290 10^# + 7) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)
PROG
(PARI) a=33; for(n=0, 1600, if(isprime(a), print1(n, ", ")); a=10*a-7)
(PARI) for(n=0, 1600, if(isprime((290*10^n+7)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Robert G. Wilson v, Aug 18 2000
EXTENSIONS
Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
Edited by N. J. A. Sloane, Apr 17 2007
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
Comments section updated and a link added by Patrick De Geest, Nov 02 2014
Edited by Ray Chandler, Nov 05 2014
STATUS
approved