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 A101521 Indices of primes in sequence defined by A(0) = 69, A(n) = 10*A(n-1) - 71 for n > 0. 1
 1, 259, 416, 952, 2137, 2968, 3044, 11776, 23647 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (550*10^n + 71)/9 is prime. Numbers n such that digit 6 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime. Numbers corresponding to terms <= 952 are certified primes. a(10) > 10^5. - Robert Price, Sep 08 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...119. FORMULA a(n) = A103029(n) - 1. EXAMPLE 619 is prime, hence 1 is a term. MATHEMATICA Select[Range[0, 10000], PrimeQ[(550*10^# + 71)/9] &] (* Robert Price, Sep 08 2015 *) PROG (PARI) a=69; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-71) (PARI) for(n=0, 1000, if(isprime((550*10^n+71)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A103029. Sequence in context: A239655 A246243 A066129 * A207060 A037987 A185673 Adjacent sequences:  A101518 A101519 A101520 * A101522 A101523 A101524 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(8)-a(9) from Kamada data by Ray Chandler, Apr 30 2015 STATUS approved

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Last modified December 14 11:52 EST 2018. Contains 318097 sequences. (Running on oeis4.)