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A101843
Indices of primes in sequence defined by A(0) = 39, A(n) = 10*A(n-1) - 11 for n > 0.
1
1, 2, 4, 5, 19, 775, 1184, 3163, 4211, 10732, 21725, 38234
OFFSET
1,2
COMMENTS
Numbers n such that (340*10^n + 11)/9 is prime.
Numbers n such that digit 3 followed by n >= 0 occurrences of digit 7 followed by digit 9 is prime.
Numbers corresponding to terms <= 775 are certified primes.
a(13) > 10^5. - Robert Price, May 08 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102977(n+1) - 1.
EXAMPLE
3779 is prime, hence 2 is a term.
MATHEMATICA
Select[Range[0, 300], PrimeQ[(340*10^# + 11)/9] &] (* Robert Price, May 08 2015 *)
PROG
(PARI) a=39; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-11)
(PARI) for(n=0, 1500, if(isprime((340*10^n+11)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(10)-a(12) from Kamada data by Ray Chandler, May 01 2015
STATUS
approved