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A101719
Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 11 for n > 0.
1
0, 1, 3, 6, 21, 22, 79, 4426, 31318, 80149, 91143
OFFSET
1,3
COMMENTS
Numbers n such that (380*10^n - 11)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime.
Numbers corresponding to terms <= 79 are certified primes.
a(12) > 10^5. - Robert Price, May 08 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102984(n) - 1.
EXAMPLE
421 is prime, hence 1 is a term.
MATHEMATICA
Select[Range[0, 3000], PrimeQ[(380*10^# - 11)/9] &] (* Robert Price, May 08 2015 *)
PROG
(PARI) a=41; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+11)
(PARI) for(n=0, 1500, if(isprime((380*10^n-11)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004
EXTENSIONS
4426 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(9) from Erik Branger May 01 2013 by Ray Chandler, Apr 30 2015
a(10)-a(11) from Robert Price, May 08 2015
STATUS
approved