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 A101847 Indices of primes in sequence defined by A(0) = 39, A(n) = 10*A(n-1) - 1 for n > 0. 1
 1, 2, 5, 16, 19, 44, 56, 77, 118, 136, 508, 709, 1126, 1517, 1760, 3085, 3146, 9925, 19853, 27841, 46798, 49681, 68717, 100541, 106648, 191072 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (350*10^n + 1)/9 is prime. Numbers n such that digit 3 followed by n >= 0 occurrences of digit 8 followed by digit 9 is prime. Numbers corresponding to terms <= 709 are certified primes. 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..26. Makoto Kamada, Prime numbers of the form 388...889. Index entries for primes involving repunits. FORMULA a(n) = A102980(n) - 1. EXAMPLE 3889 is prime, hence 2 is a term. MATHEMATICA Select[Range[0, 1000], PrimeQ[(350*10^# + 1)/9]&] PROG (PARI) a=39; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-1) (PARI) for(n=0, 1500, if(isprime((350*10^n+1)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A102980. Sequence in context: A127580 A098048 A257348 * A251600 A117557 A175735 Adjacent sequences: A101844 A101845 A101846 * A101848 A101849 A101850 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(19)-a(26) derived from A102980 by Robert Price, Mar 17 2015 STATUS approved

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Last modified September 17 23:36 EDT 2024. Contains 375991 sequences. (Running on oeis4.)