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A101972
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Indices of primes in sequence defined by A(0) = 29, A(n) = 10*A(n-1) - 1 for n > 0.
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0
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0, 6, 7, 10, 13, 18, 31, 40, 52, 60, 132, 156, 238, 1236
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OFFSET
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1,2
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COMMENTS
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Numbers n such that (260*10^n + 1)/9 is prime.
Numbers n such that digit 2 followed by n >= 0 occurrences of digit 8 followed by digit 9 is prime.
Numbers corresponding to terms <= 238 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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Table of n, a(n) for n=1..14.
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EXAMPLE
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28888889 is prime, hence 6 is a term.
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MATHEMATICA
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Flatten[Position[Table[FromDigits[Join[PadRight[{2}, n, 8], {9}]], {n, 1300}], _?PrimeQ]]-1 (* Harvey P. Dale, Sep 22 2012 *)
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PROG
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(PARI) a=29; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-1)
(PARI) for(n=0, 1500, if(isprime((260*10^n+1)/9), print1(n, ", ")))
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CROSSREFS
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Cf. A000533, A002275.
a(n) = A102963(n) - 1.
Sequence in context: A037303 A135121 A083133 * A102727 A216348 A114949
Adjacent sequences: A101969 A101970 A101971 * A101973 A101974 A101975
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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 23 2004
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STATUS
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approved
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