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 A101001 Indices of primes in sequence defined by A(0) = 91, A(n) = 10*A(n-1) + 11 for n > 0. 1
 2, 3, 23, 38, 62, 75, 107, 165, 519, 1809, 2348, 2561, 5783, 6447, 11691, 16035, 17553 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that (830*10^n - 11)/9 is prime. Numbers n such that digit 9 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime. Numbers corresponding to terms <= 519 are certified primes. a(18) > 10^5. - Robert Price, Nov 03 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..17. Makoto Kamada, Prime numbers of the form 922...221. Index entries for primes involving repunits. FORMULA a(n) = A103093(n) - 1. EXAMPLE 92221 is prime, hence 3 is a term. MATHEMATICA Select[Range[0, 100000], PrimeQ[(830*10^# - 11)/9] &] (* Robert Price, Nov 03 2015 *) PROG (PARI) a=91; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+11) (PARI) for(n=0, 1000, if(isprime((830*10^n-11)/9 ), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A103093. Sequence in context: A024773 A176892 A109615 * A231477 A215325 A215353 Adjacent sequences: A100998 A100999 A101000 * A101002 A101003 A101004 KEYWORD nonn,hard,more,less AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004 EXTENSIONS More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 a(15)-a(17) from Kamada data by Ray Chandler, Apr 28 2015 STATUS approved

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