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 A101144 Indices of primes in sequence defined by A(0) = 73, A(n) = 10*A(n-1) + 23 for n > 0. 1
 0, 3, 17, 18, 645, 813, 5793, 16523, 19494, 26009, 29237, 72119 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that (680*10^n - 23)/9 is prime. Numbers n such that digit 7 followed by n >= 0 occurrences of digit 5 followed by digit 3 is prime. Numbers corresponding to terms <= 813 are certified primes. a(13) > 10^5. - Robert Price, Oct 01 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 755...553. FORMULA a(n) = A103061(n+1) - 1. EXAMPLE 75553 is prime, hence 3 is a term. MATHEMATICA nn=5800; Transpose[Select[Thread[{NestList[10#+23&, 73, nn], Range[0, nn]}], PrimeQ[First[#]]&]][[2]] (* Harvey P. Dale, May 02 2011 *) Select[Range[0, 100000], PrimeQ[(680*10^# - 23)/9] &] (* Robert Price, Oct 01 2015 *) PROG (PARI) a=73; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+23) (PARI) for(n=0, 1000, if(isprime((680*10^n-23)/9), print1(n, ", "))) (MAGMA) [n: n in [0..100]| IsPrime((680*10^n-23) div 9)]; // Vincenzo Librandi, Oct 02 2015 CROSSREFS Cf. A000533, A002275, A103061. Sequence in context: A293764 A295395 A246143 * A038886 A019342 A029473 Adjacent sequences:  A101141 A101142 A101143 * A101145 A101146 A101147 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004 EXTENSIONS 5793 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 a(8)-a(11) from Kamada data by Ray Chandler, Apr 30 2015 a(12) from Robert Price, Oct 01 2015 STATUS approved

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Last modified May 26 22:58 EDT 2020. Contains 334634 sequences. (Running on oeis4.)