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A101534
Indices of primes in sequence defined by A(0) = 69, A(n) = 10*A(n-1) - 31 for n > 0.
1
1, 4, 7, 16, 19, 64, 82, 89, 107, 251, 334, 1487, 6355, 65711, 96797
OFFSET
1,2
COMMENTS
Numbers n such that (590*10^n + 31)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 5 followed by digit 9 is prime.
Numbers corresponding to terms <= 334 are certified primes.
Next term, if it exists, is bigger than 3000. - Stefan Steinerberger, Feb 03 2006
a(16) > 10^5. - Robert Price, Sep 13 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103041(n) - 1.
EXAMPLE
655559 is prime, hence 4 is a term.
MATHEMATICA
For[n=1, n<= 3000, n++, If[PrimeQ[(590*10^n + 31)/9], Print[n]]] (Steinerberger)
PROG
(PARI) a=69; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-31)
(PARI) for(n=0, 1500, if(isprime((590*10^n+31)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004
EXTENSIONS
More terms from Stefan Steinerberger, Feb 03 2006
6355 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(14)-a(15) from Robert Price, Sep 13 2015
STATUS
approved