A101153 Indices of primes in sequence defined by A(0) = 79, A(n) = 10*A(n-1) - 1 for n > 0.

0, 3, 17, 27, 54, 1727, 1875, 1883, 6840, 10781, 25365, 98445, 137249

Offset

1,2

Comments

Numbers n such that (710*10^n + 1)/9 is a prime.

Numbers n such that digit 7 followed by n >= 0 occurrences of digit 8 followed by digit 9 is a prime.

Numbers corresponding to terms <= 54 are certified primes.

The next term after 1883 is greater than 5000. - Ryan Propper, Jun 16 2005

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..13.

Makoto Kamada, Prime numbers of the form 788...889.

Index entries for primes involving repunits.

Formula

a(n) = A103067(n) - 1.

Example

78889 is a prime, hence 3 is a term.

Prog

(PARI) a=79; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-1)
(PARI) for(n=0, 1000, if(isprime((710*10^n+1)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103067.

Sequence in context: A273850 A060860 A273782 * A192538 A045436 A296925

Adjacent sequences: A101150 A101151 A101152 * A101154 A101155 A101156

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 03 2004

Extensions

3 more terms from Ryan Propper, Jun 16 2005

6840 from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007

a(10)-a(13) from Kamada data by Ray Chandler, Apr 23 2015

Status

approved