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A101153
Indices of primes in sequence defined by A(0) = 79, A(n) = 10*A(n-1) - 1 for n > 0.
2
0, 3, 17, 27, 54, 1727, 1875, 1883, 6840, 10781, 25365, 98445, 137249
OFFSET
1,2
COMMENTS
Numbers n such that (710*10^n + 1)/9 is a prime.
Numbers n such that digit 7 followed by n >= 0 occurrences of digit 8 followed by digit 9 is a prime.
Numbers corresponding to terms <= 54 are certified primes.
The next term after 1883 is greater than 5000. - Ryan Propper, Jun 16 2005
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103067(n) - 1.
EXAMPLE
78889 is a prime, hence 3 is a term.
PROG
(PARI) a=79; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-1)
(PARI) for(n=0, 1000, if(isprime((710*10^n+1)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004
EXTENSIONS
3 more terms from Ryan Propper, Jun 16 2005
6840 from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007
a(10)-a(13) from Kamada data by Ray Chandler, Apr 23 2015
STATUS
approved