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A101524
Indices of primes in sequence defined by A(0) = 69, A(n) = 10*A(n-1) - 61 for n > 0.
1
OFFSET
1,1
COMMENTS
Numbers n such that (560*10^n + 61)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 2 followed by digit 9 is prime.
Numbers corresponding to terms <= 338 are certified primes.
a(4) > 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) = A103031(n+1) - 1.
EXAMPLE
6229 is prime, hence 2 is a term.
MATHEMATICA
#-1&/@Transpose[Select[NestList[{First[#]+1, 10Last[#]-61}&, {1, 69}, 2000], PrimeQ[Last[#]]&]][[1]] (* Harvey P. Dale, Aug 15 2011 *)
PROG
(PARI) a=69; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-61)
(PARI) for(n=0, 1000, if(isprime((560*10^n+61)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,bref,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004
STATUS
approved