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A101138
Indices of primes in sequence defined by A(0) = 79, A(n) = 10*A(n-1) - 51 for n > 0.
1
0, 1, 4, 6, 84, 344, 1594, 2104, 6385, 9118, 9331, 14706, 72559
OFFSET
1,3
COMMENTS
Numbers n such that (660*10^n + 51)/9 is prime.
Numbers n such that digit 7 followed by n >= 0 occurrences of digit 3 followed by digit 9 is prime.
Numbers corresponding to terms <= 344 are certified primes.
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103056(n+1) - 1.
EXAMPLE
733339 is prime, hence 4 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(660*10^# + 51)/9] &] (* Robert Price, Sep 26 2015 *)
PROG
(PARI) a=79; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-51)
(PARI) for(n=0, 1000, if(isprime((660*10^n+51)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(12) from Kamada data by Ray Chandler, Apr 30 2015
a(13) from Robert Price, Sep 26 2015
STATUS
approved