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A101538
Indices of primes in sequence defined by A(0) = 63, A(n) = 10*A(n-1) + 53 for n > 0.
1
1, 2, 7, 49, 55, 71, 107, 131, 181, 1099, 1367, 1604, 5131, 22681
OFFSET
1,2
COMMENTS
Numbers n such that (620*10^n - 53)/9 is prime.
Numbers n such that digit 6 followed by n >= 0 occurrences of digit 8 followed by digit 3 is prime.
Numbers corresponding to terms <= 181 are certified primes.
a(15) > 10^5. - Robert Price, Sep 15 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A103045(n) - 1.
EXAMPLE
683 is prime, hence 1 is a term.
MATHEMATICA
Flatten[Position[NestList[10#+53&, 63, 1700], _?(PrimeQ[#]&)]]-1 (* Harvey P. Dale, Sep 24 2013 *)
PROG
(PARI) a=63; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+53)
(PARI) for(n=0, 1500, if(isprime((620*10^n-53)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(14) from Kamada data by Ray Chandler, Apr 30 2015
STATUS
approved