A101586 Indices of primes in sequence defined by A(0) = 59, A(n) = 10*A(n-1) - 11 for n > 0.

0, 2, 6, 14, 26, 128, 188, 332, 1323, 1599, 2198, 9999, 27750

Offset

1,2

Comments

Numbers n such that (520*10^n + 11)/9 is prime.

Numbers n such that digit 5 followed by n >= 0 occurrences of digit 7 followed by digit 9 is prime.

Numbers corresponding to terms <= 332 are certified primes.

a(14) > 10^5. - Robert Price, Sep 05 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..13.

Makoto Kamada, Prime numbers of the form 577...779.

Index entries for primes involving repunits.

Formula

a(n) = A103021(n+1) - 1.

Example

5779 is prime, hence 2 is a term.

Mathematica

Select[Range[0, 10000], PrimeQ[FromDigits[Join[PadRight[{5}, #+1, 7], {9}]]]&] (* Harvey P. Dale, Jan 28 2012 *)

Prog

(PARI) a=59; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-11)
(PARI) for(n=0, 1500, if(isprime((520*10^n+11)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103021.

Sequence in context: A068042 A068041 A182155 * A178080 A121968 A305329

Adjacent sequences: A101583 A101584 A101585 * A101587 A101588 A101589

Keyword

nonn

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004

Extensions

1599, 2198, 9999 from Jorge Coveiro, Dec 27 2005

a(13) from Kamada data by Ray Chandler, Apr 30 2015

Status

approved