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A101727
Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) - 13 for n > 0.
1
0, 1, 3, 4, 12, 21, 24, 27, 37, 66, 141, 283, 294, 379, 396, 1216, 1639, 2884, 3285, 7734, 29305
OFFSET
1,3
COMMENTS
Numbers n such that (410*10^n + 13)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 5 followed by digit 7 is prime.
Numbers corresponding to terms <= 396 are certified primes.
a(22) > 10^5. - Robert Price, May 22 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102992(n) - 1.
EXAMPLE
457 is prime, hence 1 is a term.
MATHEMATICA
Select[Range[0, 1000], PrimeQ[(410*10^# + 13)/9] &] (* Robert Price, May 22 2015 *)
PROG
(PARI) a=47; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-13)
(PARI) for(n=0, 1500, if(isprime((410*10^n+13)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(21) from Kamada data by Ray Chandler, Apr 30 2015
STATUS
approved