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 A101843 Indices of primes in sequence defined by A(0) = 39, A(n) = 10*A(n-1) - 11 for n > 0. 1
 1, 2, 4, 5, 19, 775, 1184, 3163, 4211, 10732, 21725, 38234 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (340*10^n + 11)/9 is prime. Numbers n such that digit 3 followed by n >= 0 occurrences of digit 7 followed by digit 9 is prime. Numbers corresponding to terms <= 775 are certified primes. a(13) > 10^5. - Robert Price, May 08 2015 REFERENCES Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. LINKS Table of n, a(n) for n=1..12. Makoto Kamada, Prime numbers of the form 377...779. Index entries for primes involving repunits. FORMULA a(n) = A102977(n+1) - 1. EXAMPLE 3779 is prime, hence 2 is a term. MATHEMATICA Select[Range[0, 300], PrimeQ[(340*10^# + 11)/9] &] (* Robert Price, May 08 2015 *) PROG (PARI) a=39; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-11) (PARI) for(n=0, 1500, if(isprime((340*10^n+11)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A102977. Sequence in context: A065063 A276311 A056440 * A192117 A084592 A101587 Adjacent sequences: A101840 A101841 A101842 * A101844 A101845 A101846 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004 EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 a(10)-a(12) from Kamada data by Ray Chandler, May 01 2015 STATUS approved

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Last modified September 10 09:32 EDT 2024. Contains 375786 sequences. (Running on oeis4.)