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 A101529 Indices of primes in sequence defined by A(0) = 67, A(n) = 10*A(n-1) - 23 for n > 0. 1
 0, 1, 4, 9, 39, 46, 57, 72, 91, 112, 123, 129, 886, 1233, 1537, 2062, 2590, 2785, 3144, 21687, 32380, 39169, 47790, 83877 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Numbers n such that (580*10^n + 23)/9 is prime. Numbers n such that digit 6 followed by n >= 0 occurrences of digit 4 followed by digit 7 is prime. Numbers corresponding to terms <= 886 are certified primes. a(25) > 10^5. - Robert Price, Sep 15 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 644...447. FORMULA a(n) = A103036(n) - 1. EXAMPLE 647 is prime, hence 1 is a term. MATHEMATICA Select[Range[0, 100000], PrimeQ[(580*10^# + 23)/9] &] (* Robert Price, Sep 15 2015 *) PROG (PARI) a=67; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-23) (PARI) for(n=0, 1500, if(isprime((580*10^n+23)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A103036. Sequence in context: A149151 A149152 A149153 * A149154 A149155 A149156 Adjacent sequences:  A101526 A101527 A101528 * A101530 A101531 A101532 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004 EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 a(20)-a(23) from Kamada data by Ray Chandler, Apr 30 2015 a(24) from Robert Price, Sep 15 2015 STATUS approved

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Last modified April 7 15:56 EDT 2020. Contains 333306 sequences. (Running on oeis4.)