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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

Table of n, a(n) for n=1..9.

Makoto Kamada, Prime numbers of the form 411...119.

Index entries for primes involving repunits.

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

Cf. A000533, A002275, A102983.

Sequence in context: A262073 A067921 A317903 * A094160 A045996 A190395

Adjacent sequences:  A101715 A101716 A101717 * A101719 A101720 A101721

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 July 13 06:56 EDT 2020. Contains 335676 sequences. (Running on oeis4.)