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A101010
Indices of primes in sequence defined by A(0) = 93, A(n) = 10*A(n-1) + 23 for n > 0.
1
1, 19, 103, 328, 1441, 1720, 24886
OFFSET
1,2
COMMENTS
Numbers n such that (860*10^n - 23)/9 is prime.
Numbers n such that digit 9 followed by n >= 0 occurrences of digit 5 followed by digit 3 is prime.
Numbers corresponding to terms <= 328 are certified primes.
a(8) > 10^5. - Robert Price, Nov 08 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103101(n+1) - 1.
EXAMPLE
953 is prime, hence 1 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(860*10^# - 23)/9] &] (* Robert Price, Nov 08 2015 *)
PROG
(PARI) a=93; for(n=0, 2000, if(isprime(a), print1(n, ", ")); a=10*a+23)
(PARI) for(n=0, 2000, if(isprime((860*10^n-23)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004
EXTENSIONS
a(7) from Kamada data by Ray Chandler, Apr 28 2015
STATUS
approved