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A101835
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Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 41 for n > 0.
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1
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0, 5, 8, 14, 23, 47, 72, 74, 96, 248, 272, 2487, 14498, 74772, 87448
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OFFSET
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1,2
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COMMENTS
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Numbers n such that (320*10^n - 41)/9 is prime.
Numbers n such that digit 3 followed by n >= 0 occurrences of digit 5 followed by digit 1 is prime.
Numbers corresponding to terms <= 272 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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3555555551 is prime, hence 8 is a term.
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MATHEMATICA
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#-1&/@Flatten[Position[NestList[10#+41&, 31, 280], _?PrimeQ]] (* Harvey P. Dale, Jul 17 2011 *)
Select[Range[0, 10000], PrimeQ[(320 10^# - 41)/9] &] (* Vincenzo Librandi, May 25 2015 *)
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PROG
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(PARI) a=31; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+41)
(PARI) for(n=0, 1500, if(isprime((320*10^n-41)/9), print1(n, ", ")))
(Magma) [n: n in [0..2000] | IsPrime((320*10^n-41) div 9)]; // Vincenzo Librandi, May 26 2015
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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 20 2004
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EXTENSIONS
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2487 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
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STATUS
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approved
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