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A101012
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Indices of primes in sequence defined by A(0) = 91, A(n) = 10*A(n-1) + 51 for n > 0.
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1
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2, 3, 4, 5, 7, 15, 33, 40, 51, 88, 104, 321, 634, 939, 943, 1130, 1197, 1742, 1871, 37913, 41655, 90095, 99473
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OFFSET
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1,1
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COMMENTS
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Numbers n such that (870*10^n - 51)/9 is prime.
Numbers n such that digit 9 followed by n >= 0 occurrences of digit 6 followed by digit 1 is prime.
Numbers corresponding to terms <= 1130 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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96661 is prime, hence 3 is a term.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(290*10^# - 17)/3] &] (* Robert Price, Jan 10 2017 *)
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PROG
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(PARI) a=91; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+51)
(PARI) for(n=0, 1500, if(isprime((870*10^n-51)/9), print1(n, ", ")))
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CROSSREFS
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KEYWORD
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nonn,hard,more
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AUTHOR
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Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004
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EXTENSIONS
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More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
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STATUS
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approved
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