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A102028
Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 11 for n > 0.
1
0, 1, 7, 9, 24, 49, 75, 103, 4405, 8934, 25999, 31651
OFFSET
1,3
COMMENTS
Numbers n such that (160*10^n + 11)/9 is prime.
Numbers n such that digit 1 followed by n >= 0 occurrences of digit 7 followed by digit 9 is prime.
Numbers corresponding to terms <= 103 are certified primes.
a(13) > 10^5. - Robert Price, Feb 07 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102943(n) - 1.
EXAMPLE
179 is prime, hence 1 is a term.
PROG
(PARI) a=19; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-11)
(PARI) for(n=0, 1500, if(isprime((160*10^n+11)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(11)-a(12) derived from A102943 by Robert Price, Feb 07 2015
STATUS
approved