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 A101523 Indices of primes in sequence defined by A(0) = 67, A(n) = 10*A(n-1) - 43 for n > 0. 1
 0, 12, 72, 126 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (560*10^n + 43)/9 is prime. Numbers n such that digit 6 followed by n >= 0 occurrences of digit 2 followed by digit 7 is prime. Numbers corresponding to terms <= 126 are certified primes. a(5) > 10^5. - Robert Price, Sep 12 2015 REFERENCES Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. LINKS Makoto Kamada, Prime numbers of the form 622...227. FORMULA a(n) = A097402(n+1) - 1. EXAMPLE 67 is prime, hence 0 is a term. MATHEMATICA Select[Range[0, 100000], PrimeQ[(560 * 10^# + 43)/9] &] (* Robert Price, Sep 12 2015 *) PROG (PARI) a=67; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-43) (PARI) for(n=0, 1000, if(isprime((560*10^n+43)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A097402. Sequence in context: A209447 A219302 A338261 * A340302 A143698 A304164 Adjacent sequences:  A101520 A101521 A101522 * A101524 A101525 A101526 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004 STATUS approved

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Last modified July 29 17:41 EDT 2021. Contains 346346 sequences. (Running on oeis4.)