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A101722 Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 61 for n > 0. 1
2, 2042, 5966, 39854 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that (380*10^n + 61)/9 is prime.

Numbers n such that digit 4 followed by n >= 0 occurrences of digit 2 followed by digit 9 is prime.

Some of the larger entries may only correspond to probable primes.

Certified primality of number corresponding to term 2042 using Primo. - Ryan Propper, Jun 23 2005

a(5) > 10^5. - Robert Price, May 08 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 422...229.

Index entries for primes involving repunits.

FORMULA

a(n) = A102987(n+1) - 1.

EXAMPLE

4229 is prime, hence 2 is a term.

MATHEMATICA

Select[Range[0, 3000], PrimeQ[(380*10^# + 61)/9] &] (* Robert Price, May 08 2015 *)

PROG

(PARI) a=49; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-61)

(PARI) for(n=0, 1500, if(isprime((380*10^n+61)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A102987.

Sequence in context: A124361 A166339 A024034 * A004908 A275002 A004813

Adjacent sequences:  A101719 A101720 A101721 * A101723 A101724 A101725

KEYWORD

nonn,bref,hard,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004

EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007

a(4) from Kamada link by Ray Chandler, Apr 24 2015

STATUS

approved

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Last modified September 27 16:20 EDT 2020. Contains 337383 sequences. (Running on oeis4.)