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 A056249 Indices of primes in sequence defined by A(0) = 11, A(n) = 10*A(n-1) + 71 for n > 0. 2
 0, 1, 7, 13, 39, 91, 127, 883, 9423, 14767, 19257, 31233 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Numbers n such that (170*10^n - 71)/9 is prime. Numbers n such that digit 1 followed by n >= 0 occurrences of digit 8 followed by digit 1 is prime. Numbers corresponding to terms <= 883 are certified primes. REFERENCES Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467. LINKS Patrick De Geest, PDP Reference Table - 181. Makoto Kamada, Prime numbers of the form 188...881. FORMULA a(n) = A082702(n-1) - 2 for n > 1. EXAMPLE 181 is prime, hence 1 is a term. MATHEMATICA Select[Range[0, 2000], PrimeQ[(170 10^# - 71) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *) PROG (PARI) a=11; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+71) (PARI) for(n=0, 1500, if(isprime((170*10^n-71)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A068648, A082702. Sequence in context: A144729 A123250 A062591 * A107207 A045464 A134854 Adjacent sequences:  A056246 A056247 A056248 * A056250 A056251 A056252 KEYWORD nonn,hard,more,changed AUTHOR Robert G. Wilson v, Aug 18 2000 EXTENSIONS Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004 Edited by N. J. A. Sloane, Jun 15 2007 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008 Updated and added a link, by Patrick De Geest, Nov 02 2014 Edited by Ray Chandler, Nov 04 2014 STATUS approved

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Last modified January 18 04:47 EST 2019. Contains 319269 sequences. (Running on oeis4.)