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A101718 Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 71 for n > 0. 1
1, 4, 76, 205, 1870, 3886, 11581, 20233, 60289 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Numbers n such that (370*10^n + 71)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 1 followed by digit 9 is prime.
a(10) > 10^5. - Robert Price, Apr 14 2015
REFERENCES
Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
LINKS
FORMULA
a(n) = A102983(n) - 1.
EXAMPLE
411119 is prime, hence 4 is a term.
MATHEMATICA
Select[Range[0, 2000], PrimeQ[(370*10^# + 71)/9] &] (* Robert Price, Apr 14 2015 *)
PROG
(PARI) a=49; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-71)
(PARI) for(n=0, 1500, if(isprime((370*10^n+71)/9), print1(n, ", ")))
(Magma) [n: n in [0..300] | IsPrime((370*10^n+71) div 9)]; // Vincenzo Librandi, Apr 15 2015
CROSSREFS
Sequence in context: A262073 A067921 A317903 * A094160 A045996 A190395
KEYWORD
nonn,hard,more
AUTHOR
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004
EXTENSIONS
3886 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(7)-a(9) derived from A102983 by Robert Price, Apr 14 2015
STATUS
approved

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Last modified March 19 01:57 EDT 2024. Contains 370952 sequences. (Running on oeis4.)