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A101523 Indices of primes in sequence defined by A(0) = 67, A(n) = 10*A(n-1) - 43 for n > 0. 1
0, 12, 72, 126 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (560*10^n + 43)/9 is prime.

Numbers n such that digit 6 followed by n >= 0 occurrences of digit 2 followed by digit 7 is prime.

Numbers corresponding to terms <= 126 are certified primes.

a(5) > 10^5. - Robert Price, Sep 12 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..4.

Makoto Kamada, Prime numbers of the form 622...227.

Index entries for primes involving repunits.

FORMULA

a(n) = A097402(n+1) - 1.

EXAMPLE

67 is prime, hence 0 is a term.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(560 * 10^# + 43)/9] &] (* Robert Price, Sep 12 2015 *)

PROG

(PARI) a=67; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-43)

(PARI) for(n=0, 1000, if(isprime((560*10^n+43)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A097402.

Sequence in context: A209447 A219302 A338261 * A340302 A143698 A304164

Adjacent sequences:  A101520 A101521 A101522 * A101524 A101525 A101526

KEYWORD

nonn,hard,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 06 2004

STATUS

approved

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Last modified July 29 17:41 EDT 2021. Contains 346346 sequences. (Running on oeis4.)