login
A101060
Indices of primes in sequence defined by A(0) = 89, A(n) = 10*A(n-1) - 71 for n > 0.
1
0, 3, 6, 8, 18, 21, 69, 101, 120, 122, 234, 359, 593, 1613, 2409, 16047, 16173
OFFSET
1,2
COMMENTS
Numbers n such that (730*10^n + 71)/9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime.
Numbers corresponding to terms <= 593 are certified primes.
a(18) > 10^5. - Robert Price, Oct 13 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103073(n) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
EXAMPLE
81119 is prime, hence 3 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(730*10^# + 71)/9] &] (* Robert Price, Oct 13 2015 *)
PROG
(PARI) a=89; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-71)
(PARI) for(n=0, 1000, if(isprime((730*10^n+71)/9), print1(n, ", ")))
(Magma) [n: n in [0..400] | IsPrime((730*10^n+71) div 9)]; // Vincenzo Librandi, Oct 14 2015
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(16)-a(17) from Kamada data by Ray Chandler, Apr 29 2015
STATUS
approved