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A056260
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Indices of primes in sequence defined by A(0) = 77, A(n) = 10*A(n-1) - 3 for n > 0. Numbers n such that (690*10^n + 3)/9 is prime.
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2
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3, 5, 53, 95, 453, 573, 3383, 11439, 12623, 19445, 35459, 81213, 95325
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OFFSET
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1,1
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COMMENTS
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Numbers n such that digit 7 followed by n >= 0 occurrences of digit 6 followed by digit 7 is prime.
Numbers corresponding to terms <= 3383 are certified primes.
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REFERENCES
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Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
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LINKS
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FORMULA
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EXAMPLE
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76667 is prime, hence 3 is a term.
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MATHEMATICA
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Select[Range[3500], PrimeQ[(690 10^# + 3) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)
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PROG
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(PARI) a=77; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-3)
(PARI) for(n=0, 1000, if(isprime((690*10^n+3)/9), print1(n, ", ")))
(Magma) [n: n in [0..300] | IsPrime((690*10^n+3) div 9)]; // Vincenzo Librandi, Nov 03 2014
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CROSSREFS
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KEYWORD
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hard,nonn
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AUTHOR
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EXTENSIONS
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Two more terms added from PDP Table, a link added and comments section updated by Patrick De Geest, Nov 02 2014
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STATUS
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approved
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