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 A101016 Indices of primes in sequence defined by A(0) = 91, A(n) = 10*A(n-1) + 71 for n > 0. 1
 5, 8, 89, 110, 209, 236, 413, 1191, 1259, 5835, 6771, 24860, 52430 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that (890*10^n - 71)/9 is prime. Numbers n such that digit 9 followed by n >= 0 occurrences of digit 8 followed by digit 1 is prime. Numbers corresponding to terms <= 413 are certified primes. Certified primality of terms corresponding to 1191 and 1259 with Primo. - Ryan Propper, Jun 20 2005 a(14) > 10^5. - Robert Price, Nov 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 988...881. FORMULA a(n) = A103107(n+1) - 1. EXAMPLE 9888881 is prime, hence 5 is a term. MATHEMATICA Select[Range[0, 100000], PrimeQ[(890*10^# - 71)/9] &] (* Robert Price, Nov 12 2015 *) PROG (PARI) a=91; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+71) (PARI) for(n=0, 1500, if(isprime((890*10^n-71)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A103107. Sequence in context: A123819 A260695 A153720 * A264295 A025518 A267003 Adjacent sequences:  A101013 A101014 A101015 * A101017 A101018 A101019 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004 EXTENSIONS Two additional terms, corresponding to probable primes, from Ryan Propper, Jun 20 2005 Edited by T. D. Noe, Oct 30 2008 a(12) from Kamada data by Ray Chandler, Apr 29 2015 a(13) from Robert Price, Nov 12 2015 STATUS approved

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