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 A101520 Indices of primes in sequence defined by A(0) = 67, A(n) = 10*A(n-1) - 53 for n > 0. 1
 0, 1, 31, 42, 972, 1194, 4470, 5683, 7987, 46884 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Numbers n such that (550*10^n + 53)/9 is prime. Numbers n such that digit 6 followed by n >= 0 occurrences of digit 1 followed by digit 7 is prime. Numbers corresponding to terms <= 972 are certified primes. a(11) > 10^5. - Robert Price, Sep 07 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 611...117. FORMULA a(n) = A103028(n) - 1. EXAMPLE 67 is prime, hence 0 is a term. MATHEMATICA Select[Range[0, 10000], PrimeQ[(550*10^# + 53)/9] &] (* Robert Price, Sep 07 2015 *) PROG (PARI) a=67; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-53) (PARI) for(n=0, 1500, if(isprime((550*10^n+53)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A103028. Sequence in context: A040180 A158754 A140458 * A225862 A089713 A281246 Adjacent sequences:  A101517 A101518 A101519 * A101521 A101522 A101523 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(10) from Erik Branger May 01 2013 by Ray Chandler, Apr 30 2015 STATUS approved

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Last modified October 17 12:33 EDT 2019. Contains 328112 sequences. (Running on oeis4.)