A101580 Indices of primes in sequence defined by A(0) = 57, A(n) = 10*A(n-1) - 23 for n > 0.

1, 5, 7, 17, 52, 67, 241, 275, 319, 563, 619, 1781, 2339, 2453, 5764, 15529, 15604, 22937

Offset

1,2

Comments

Numbers n such that (490*10^n + 23)/9 is prime.

Numbers n such that digit 5 followed by n >= 0 occurrences of digit 4 followed by digit 7 is prime.

a(19) > 10^5. - Robert Price, Jul 29 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..18.

Makoto Kamada, Prime numbers of the form 544...447.

Index entries for primes involving repunits.

Formula

a(n) = A103015(n) - 1.

Example

547 is prime, hence 1 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(490*10^# + 23)/9] &] (* Robert Price, Ju1 29 2015 *)

Prog

(PARI) a=57; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a-23)
(PARI) for(n=0, 1000, if(isprime((490*10^n+23)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103015.

Sequence in context: A019404 A248085 A079604 * A190663 A123195 A248480

Adjacent sequences: A101577 A101578 A101579 * A101581 A101582 A101583

Keyword

nonn,more

Author

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

Extensions

Three additional terms, corresponding to probable primes, from Ryan Propper, Jun 18 2005

5764 from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007

Edited by T. D. Noe, Oct 30 2008

a(16)-a(18) by Ray Chandler, Apr 24 2015

Status

approved