OFFSET
1,2
COMMENTS
Numbers n such that (110*10^n + 7)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 2 followed by digit 3 is prime.
Numbers corresponding to terms <= 875 are certified primes.
a(13) > 10^5. - Robert Price, Nov 15 2014
a(13) > 2*10^5. - Tyler Busby, Feb 01 2023
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A102929(n+1) - 1. - Robert Price, Nov 15 2014
EXAMPLE
1223 is prime, hence 2 is a term.
PROG
(PARI) a=13; for(n=0, 1600, if(isprime(a), print1(n, ", ")); a=10*a-7)
(PARI) for(n=0, 1600, if(isprime((110*10^n+7)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
EXTENSIONS
a(11)-a(12) derived from A102929 by Robert Price, Nov 15 2014
STATUS
approved