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A056251
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Indices of primes in sequence defined by A(0) = 33, A(n) = 10*A(n-1) - 17 for n > 0.
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3
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OFFSET
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1,2
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COMMENTS
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Numbers n such that (280*10^n + 17)/9 is prime.
Numbers n such that digit 3 followed by n >= 0 occurrences of digit 1 followed by digit 3 is prime.
Numbers corresponding to terms <= 599 are certified primes.
All terms are odd since 11 is the only palindromic prime with an even number of digits. - Chai Wah Wu, Nov 05 2019
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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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313 is prime, hence 1 is a term.
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MATHEMATICA
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Flatten[Position[NestList[10#-17&, 33, 600], _?PrimeQ]-1] (* This generates the first 8 terms of the sequence. Changing the last constant from 600 to 9825 will generate all 9 terms of the sequence but it will take a long time to do so. - Harvey P. Dale, May 16 2012 *)
Select[Range[0, 2000], PrimeQ[(280 10^# + 17) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)
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PROG
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(PARI) a=33; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-17)
(PARI) for(n=0, 1500, if(isprime((280*10^n+17)/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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EXTENSIONS
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Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
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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