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A101952 Indices of primes in sequence defined by A(0) = 29, A(n) = 10*A(n-1) - 81 for n > 0. 1
0, 4, 24, 454, 760, 9204, 13560, 15954, 26668, 113940 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Numbers n such that 20*10^n + 9 is prime.
Numbers n such that digit 2 followed by n >= 0 occurrences of digit 0 followed by digit 9 is prime.
Numbers corresponding to terms <= 760 are certified primes.
a(11) > 2*10^5. - Robert Price, Jun 06 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A101392(n-1) - 1. - Robert Price, Nov 25 2014
EXAMPLE
200009 is prime, hence 4 is a term.
MATHEMATICA
Select[Range[0, 300], PrimeQ[20*10^# + 9] &] (* Robert Price, Jun 06 2015 *)
PROG
(PARI) a=29; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-81)
(PARI) for(n=0, 1500, if(isprime(20*10^n+9), print1(n, ", ")))
CROSSREFS
Sequence in context: A296398 A166947 A103624 * A009535 A139096 A111425
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(9)-a(10) derived from A101392 by Robert Price, Nov 25 2014
STATUS
approved

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Last modified April 23 07:11 EDT 2024. Contains 371905 sequences. (Running on oeis4.)