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 A101733 Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 11 for n > 0. 1
 1, 3, 25, 1270, 1411, 3327, 4675, 47050, 67663 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (430*10^n + 11)/9 is a prime. Numbers n such that digit 4 followed by n >= 0 occurrences of digit 7 followed by digit 9 is a prime. Some of the larger entries may only correspond to probable primes. a(10) > 10^5. - Robert Price, Jun 01 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 477...779. FORMULA a(n) = A102996(n) - 1. EXAMPLE 47779 is a prime, hence 3 is a term. MATHEMATICA Select[Range[0, 1000], PrimeQ[(430*10^# + 11)/9] &] (* Robert Price, Jun 01 2015 *) PROG (PARI) a=49; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-11) (PARI) for(n=0, 1500, if(isprime((430*10^n+11)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A102996. Sequence in context: A306792 A012764 A219275 * A309116 A094815 A246536 Adjacent sequences:  A101730 A101731 A101732 * A101734 A101735 A101736 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004 EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 a(8) from Erik Branger May 01 2013 by Ray Chandler, May 01 2015 a(9) from Robert Price, Jun 01 2015 STATUS approved

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Last modified July 17 14:44 EDT 2019. Contains 325106 sequences. (Running on oeis4.)