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A101574
Indices of primes in sequence defined by A(0) = 53, A(n) = 10*A(n-1) - 7 for n > 0.
1
0, 1, 3, 6, 102, 165, 279, 474, 504, 834, 921, 2017, 4434, 4458, 7614, 8557, 17163, 22800
OFFSET
1,3
COMMENTS
Numbers n such that (470*10^n + 7)/9 is prime.
Numbers n such that digit 5 followed by n >= 0 occurrences of digit 2 followed by digit 3 is prime.
Numbers corresponding to terms <= 921 are certified primes.
a(19) > 10^5. - Robert Price, Jul 10 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103009(n) - 1.
EXAMPLE
52223 is prime, hence 3 is a term.
PROG
(PARI) a=53; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-7)
(PARI) for(n=0, 1500, if(isprime((470*10^n+7)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(17)-a(18) from Kamada data by Ray Chandler, Apr 30 2015
STATUS
approved