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A101571
Indices of primes in sequence defined by A(0) = 57, A(n) = 10*A(n-1) - 53 for n > 0.
1
22, 52, 12808, 15070
OFFSET
1,1
COMMENTS
Numbers n such that (460*10^n + 53)/9 is prime.
Numbers n such that digit 5 followed by n >= 0 occurrences of digit 1 followed by digit 7 is prime.
Numbers corresponding to terms <= 52 are certified primes. No further terms up to 2400.
a(5) > 10^5. - Robert Price, Jun 20 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103006(n+1) - 1.
EXAMPLE
511111111111111111111117 is prime, hence 22 is a term.
PROG
(PARI) a=57; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-53)
(PARI) for(n=0, 1000, if(isprime((460*10^n+53)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004
EXTENSIONS
a(3)-a(4) from Kamada data by Ray Chandler, Apr 30 2015
STATUS
approved