OFFSET
1,2
COMMENTS
Numbers n such that (110*10^n + 61)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 2 followed by digit 9 is prime.
Numbers corresponding to terms <= 546 are certified primes.
a(13) > 10^5. - Robert Price, Jan 17 2015
a(15) > 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) = A102931(n) - 1.
EXAMPLE
1222229 is prime, hence 5 is a term.
PROG
(PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-61)
(PARI) for(n=0, 1500, if(isprime((110*10^n+61)/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 A102931 by Robert Price, Jan 17 2015
a(13)-a(14) from Tyler Busby, Jan 31 2023
STATUS
approved