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A101970
Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) + 53 for n > 0.
1
0, 1, 6, 27, 72, 294, 493, 597, 2599, 3729, 7548, 15864
OFFSET
1,3
COMMENTS
Numbers n such that (260*10^n - 53)/9 is prime.
Numbers n such that digit 2 followed by n >= 0 occurrences of digit 8 followed by digit 3 is prime.
Numbers corresponding to terms <= 597 are certified primes.
a(13) > 10^5. - Robert Price, Apr 18 2014
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
FORMULA
a(n) = A102961(n) - 1. [adapted by Georg Fischer, Jan 04 2021]
EXAMPLE
283 is prime, hence 1 is a term.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(260*10^# - 53)/9] &] (* Robert Price, Apr 18 2015 *)
PROG
(PARI) a=23; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+53)
(PARI) for(n=0, 1500, if(isprime((260*10^n-53)/9), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(12) derived from A102961 by Robert Price, Apr 18 2015
STATUS
approved