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A101069
Indices of primes in sequence defined by A(0) = 89, A(n) = 10*A(n-1) - 41 for n > 0.
1
0, 3, 12, 36, 45, 105, 138, 468, 5694, 56280, 58669
OFFSET
1,2
COMMENTS
Numbers n such that (760*10^n + 41)/9 is prime.
Numbers n such that digit 8 followed by n >= 0 occurrences of digit 4 followed by digit 9 is prime.
Numbers corresponding to terms <= 468 are certified primes.
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103082(n+1) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
EXAMPLE
84449 is prime, hence 3 is a term.
MATHEMATICA
Select[Range[0, 5700], PrimeQ[FromDigits[Join[PadRight[{8}, #+1, 4], {9}]]]&] (* Harvey P. Dale, Jan 23 2012 *)
PROG
(PARI) a=89; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-41)
(PARI) for(n=0, 1000, if(isprime((760*10^n+41)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 30 2004
EXTENSIONS
One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(10)-a(11) from Robert Price, Oct 18 2015
STATUS
approved