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 A101736 Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) + 17 for n > 0. 1
 0, 1, 6, 13, 24, 115, 426, 594, 636, 775, 1705, 16627, 55557 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Numbers n such that (440*10^n - 17)/9 is prime. Numbers n such that digit 4 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime. Numbers corresponding to terms <= 775 are certified primes. a(14) > 10^5. - Robert Price, Jun 05 2015 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..13. Makoto Kamada, Prime numbers of the form 488...887. Index entries for primes involving repunits. FORMULA a(n) = A102999(n) - 1. EXAMPLE 487 is prime, hence 1 is a term. MATHEMATICA For[n=0, n<= 3000, n++, If[PrimeQ[(440*10^n - 17)/9], Print[n]]] (Steinerberger) PROG (PARI) a=47; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+17) (PARI) for(n=0, 1500, if(isprime((440*10^n-17)/9), print1(n, ", "))) CROSSREFS Cf. A000533, A002275, A102999. Sequence in context: A032528 A058535 A131833 * A162432 A117072 A081395 Adjacent sequences: A101733 A101734 A101735 * A101737 A101738 A101739 KEYWORD nonn,hard AUTHOR Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004 EXTENSIONS a(11) from Stefan Steinerberger, Feb 04 2006 a(12) from Kamada data by Ray Chandler, May 01 2015 a(13) from Robert Price, Jun 05 2015 STATUS approved

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Last modified September 15 10:10 EDT 2024. Contains 375932 sequences. (Running on oeis4.)