OFFSET
1,2
COMMENTS
Numbers n such that (250*10^n + 11)/9 is a prime.
Numbers n such that digit 2 followed by n >= 0 occurrences of digit 7 followed by digit 9 is a prime.
Numbers corresponding to terms <= 215 are certified primes.
a(16) > 10^5. - Robert Price, Mar 12 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A102959(n) - 1.
EXAMPLE
27779 is a prime, hence 3 is a term.
MATHEMATICA
Flatten[Position[NestList[10#-11&, 29, 1500], _?PrimeQ]]-1 (* Harvey P. Dale, Oct 14 2013 *)
PROG
(PARI) a=29; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-11)
(PARI) for(n=0, 1500, if(isprime((250*10^n+11)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
A(11)-a(15) derived from A102959 by Robert Price, Mar 12 2015
STATUS
approved