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 A101972 Indices of primes in sequence defined by A(0) = 29, A(n) = 10*A(n-1) - 1 for n > 0. 0
 0, 6, 7, 10, 13, 18, 31, 40, 52, 60, 132, 156, 238, 1236 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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. REFERENCES Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. LINKS EXAMPLE 28888889 is prime, hence 6 is a term. MATHEMATICA Flatten[Position[Table[FromDigits[Join[PadRight[{2}, n, 8], {9}]], {n, 1300}], _?PrimeQ]]-1 (* Harvey P. Dale, Sep 22 2012 *) PROG (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, ", "))) CROSSREFS 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 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004 STATUS approved

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