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A101724
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Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) - 33 for n > 0.
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2
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0, 2, 4, 5, 7, 14, 25, 52, 59, 96, 182, 204, 301, 395, 455, 466, 606, 827, 1859, 2742, 4272, 4780, 5711, 6037, 6636, 9221, 10831, 18864, 25847, 42246, 48546, 87564, 95587
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OFFSET
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1,2
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COMMENTS
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Numbers n such that (390*10^n + 33)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 3 followed by digit 7 is prime.
Numbers corresponding to terms <= 827 are certified primes.
a(34) > 10^5. - Robert Price, May 11 2015
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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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4337 is prime, hence 2 is a term.
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MATHEMATICA
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Select[Range[0, 300], PrimeQ[(390*10^# + 33)/9] &] (* Robert Price, May 11 2015 *)
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PROG
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(PARI) a=47; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-33)
(PARI) for(n=0, 1500, if(isprime((390*10^n+33)/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), Dec 14 2004
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EXTENSIONS
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More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
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STATUS
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approved
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