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 A101835 Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 41 for n > 0. 1
 0, 5, 8, 14, 23, 47, 72, 74, 96, 248, 272, 2487, 14498, 74772, 87448 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (320*10^n - 41)/9 is prime. Numbers n such that digit 3 followed by n >= 0 occurrences of digit 5 followed by digit 1 is prime. Numbers corresponding to terms <= 272 are certified primes. a(16) > 10^5. - Robert Price, May 24 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 355...551. FORMULA a(n) = A102971(n) - 1. EXAMPLE 3555555551 is prime, hence 8 is a term. MATHEMATICA #-1&/@Flatten[Position[NestList[10#+41&, 31, 280], _?PrimeQ]] (* Harvey P. Dale, Jul 17 2011 *) Select[Range[0, 10000], PrimeQ[(320 10^# - 41)/9] &] (* Vincenzo Librandi, May 25 2015 *) PROG (PARI) a=31; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+41) (PARI) for(n=0, 1500, if(isprime((320*10^n-41)/9), print1(n, ", "))) (MAGMA) [n: n in [0..2000] | IsPrime((320*10^n-41) div 9)]; // Vincenzo Librandi, May 26 2015 CROSSREFS Cf. A000533, A002275, A102971. Sequence in context: A092590 A065394 A124011 * A192522 A133641 A164094 Adjacent sequences:  A101832 A101833 A101834 * A101836 A101837 A101838 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004 EXTENSIONS 2487 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 a(13) from Kamada data by Ray Chandler, May 01 2015 a(14)-a(15) from Robert Price, May 24 2015 STATUS approved

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Last modified April 15 02:49 EDT 2021. Contains 342974 sequences. (Running on oeis4.)