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A101588
Indices of primes in sequence defined by A(0) = 57, A(n) = 10*A(n-1) + 17 for n > 0.
1
1, 5, 7, 19, 107, 287, 305, 461, 20101, 30041, 69049
OFFSET
1,2
COMMENTS
Numbers n such that (530*10^n - 17)/9 is prime.
Numbers n such that digit 5 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime.
Numbers corresponding to terms <= 461 are certified primes.
a(12) > 10^5. - Robert Price, Sep 07 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103023(n) - 1.
EXAMPLE
587 is prime, hence 1 is a term.
MATHEMATICA
Select[Range[0, 300], PrimeQ[(530*10^# - 17)/9] &] (* Robert Price, Sep 07 2015 *)
PROG
(PARI) a=57; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+17)
(PARI) for(n=0, 1000, if(isprime((530*10^n-17)/9), print1(n, ", ")))
(Magma) [n: n in [0..350] | IsPrime((530*10^n-17) div 9 )]; // Vincenzo Librandi, Sep 08 2015
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004
EXTENSIONS
a(9)-a(10) from Kamada data by Ray Chandler, Apr 30 2015
a(11) from Robert Price, Sep 07 2015
STATUS
approved