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A101536
Indices of primes in sequence defined by A(0) = 69, A(n) = 10*A(n-1) - 11 for n > 0.
1
2, 4, 14, 46, 68, 122, 712, 2315, 6146, 8876, 10703
OFFSET
1,1
COMMENTS
Numbers n such that (610*10^n + 11)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 7 followed by digit 9 is prime.
Numbers corresponding to terms <= 712 are certified primes.
a(12) > 10^5. - Robert Price, Sep 15 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103043(n) - 1.
EXAMPLE
6779 is prime, hence 2 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(610*10^# + 11)/9] &] (* Robert Price, Sep 15 2015 *)
PROG
(PARI) a=69; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-11)
(PARI) for(n=0, 1000, if(isprime((610*10^n+11)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(11) from Kamada data by Ray Chandler, Apr 30 2015
STATUS
approved