A101585 Indices of primes in sequence defined by A(0) = 53, A(n) = 10*A(n-1) + 43 for n > 0.

0, 3, 11, 14, 17, 36, 108, 1727, 2481, 3479, 6576, 9014, 16161, 45348

Offset

1,2

Comments

Numbers n such that (520*10^n - 43)/9 is prime.

Numbers n such that digit 5 followed by n >= 0 occurrences of digit 7 followed by digit 3 is prime.

Numbers corresponding to terms <= 108 are certified primes.

a(15) > 10^5. - Robert Price, Sep 09 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..14.

Makoto Kamada, Prime numbers of the form 577...773.

Index entries for primes involving repunits.

Formula

a(n) = A103020(n) - 1.

Example

57773 is prime, hence 3 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(520*10^# - 43)/9] &] (* Robert Price, Sep 09 2015 *)

Prog

(PARI) a=53; for(n=0, 1000, if(isprime(a), print1(n, ", ")); a=10*a+43)
(PARI) for(n=0, 1000, if(isprime((520*10^n-43)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103020.

Sequence in context: A224857 A322608 A063963 * A115214 A143029 A186701

Adjacent sequences: A101582 A101583 A101584 * A101586 A101587 A101588

Keyword

nonn,more

Author

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

Extensions

Five additional terms, corresponding to probable primes, from Ryan Propper, Jun 22 2005

Edited by T. D. Noe, Oct 30 2008

a(13)-a(14) from Kamada data by Ray Chandler, Apr 30 2015

Status

approved