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 A101530 Indices of primes in sequence defined by A(0) = 69, A(n) = 10*A(n-1) - 41 for n > 0. 1
 2, 104, 626, 686, 698, 5714, 11390, 11672 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that (580*10^n + 41)/9 is prime. Numbers n such that digit 6 followed by n >= 0 occurrences of digit 4 followed by digit 9 is prime. Numbers corresponding to terms <= 698 are certified primes. a(9) > 10^5. - Robert Price, Sep 11 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 644...449. FORMULA a(n) = A103037(n+1) - 1. EXAMPLE 6449 is prime, hence 2 is a term. MATHEMATICA Select[Range[0, 100000], PrimeQ[(580*10^# + 41)/9] &] (* Robert Price, Sep 11 2015 *) PROG (PARI) a=69; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-41) (PARI) for(n=0, 1000, if(isprime((580*10^n+41)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A103037. Sequence in context: A176933 A246775 A281053 * A199945 A265655 A001184 Adjacent sequences:  A101527 A101528 A101529 * A101531 A101532 A101533 KEYWORD nonn,hard,more AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004 EXTENSIONS 5714 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008 a(7)-a(8) from Kamada data by Ray Chandler, Apr 30 2015 STATUS approved

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Last modified March 30 12:10 EDT 2020. Contains 333125 sequences. (Running on oeis4.)