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 A102031 Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 1 for n > 0. 2
 0, 2, 11, 266, 842, 6299, 37991, 54116, 121241, 121620 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (170*10^n + 1)/9 is prime. Numbers n such that digit 1 followed by n >= 0 occurrences of digit 8 followed by digit 9 is prime. Numbers corresponding to terms <= 842 are certified primes. a(11) > 2*10^5. - Robert Price, Nov 16 2014 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 188...889. FORMULA a(n) = A102945(n) - 1. EXAMPLE 1889 is prime, hence 2 is a term. MAPLE A102031:=n->`if`(isprime((170*10^n+1)/9), n, NULL): seq(A102031(n), n=0..10^3); # Wesley Ivan Hurt, Nov 16 2014 MATHEMATICA Select[Range[0, 10^3], PrimeQ[(170*10^# + 1)/9] &] (* Wesley Ivan Hurt, Nov 16 2014 *) PROG (PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-1) (PARI) for(n=0, 1500, if(isprime((170*10^n+1)/9), print1(n, ", "))) (MAGMA) [n: n in [0..300] | IsPrime((170*10^n+1) div 9)]; // Vincenzo Librandi, Nov 17 2014 CROSSREFS Cf. A000533, A002275, A102945. Sequence in context: A264330 A134096 A132571 * A248865 A072386 A185122 Adjacent sequences:  A102028 A102029 A102030 * A102032 A102033 A102034 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004 EXTENSIONS 6299 from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 22 2007 a(7)-a(10) added by Max Alekseyev, Dec 12 2011 STATUS approved

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Last modified January 18 16:27 EST 2020. Contains 331011 sequences. (Running on oeis4.)