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A101733
Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 11 for n > 0.
1
1, 3, 25, 1270, 1411, 3327, 4675, 47050, 67663
OFFSET
1,2
COMMENTS
Numbers n such that (430*10^n + 11)/9 is a prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 7 followed by digit 9 is a prime.
Some of the larger entries may only correspond to probable primes.
a(10) > 10^5. - Robert Price, Jun 01 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102996(n) - 1.
EXAMPLE
47779 is a prime, hence 3 is a term.
MATHEMATICA
Select[Range[0, 1000], PrimeQ[(430*10^# + 11)/9] &] (* Robert Price, Jun 01 2015 *)
PROG
(PARI) a=49; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-11)
(PARI) for(n=0, 1500, if(isprime((430*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
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(8) from Erik Branger May 01 2013 by Ray Chandler, May 01 2015
a(9) from Robert Price, Jun 01 2015
STATUS
approved