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A101068
Indices of primes in sequence defined by A(0) = 87, A(n) = 10*A(n-1) - 23 for n > 0.
1
2, 4, 100, 104, 4096, 5732, 9754, 31832
OFFSET
1,1
COMMENTS
Numbers n such that (760*10^n + 23)/9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 4 followed by digit 7 is prime.
Numbers corresponding to terms <= 104 are certified primes.
a(9) > 10^5. - Robert Price, Oct 18 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103081(n+1) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
EXAMPLE
8447 is prime, hence 2 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(760*10^# + 23)/9] &] (* Robert Price, Oct 18 2015 *)
PROG
(PARI) a=87; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-23)
(PARI) for(n=0, 1000, if(isprime((760*10^n + 23)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 30 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(8) from Erik Branger May 01 2013 by Ray Chandler, Apr 29 2015
STATUS
approved