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A056255 Indices of primes in sequence defined by A(0) = 33, A(n) = 10*A(n-1) + 43 for n > 0. 1
1, 13, 53, 67, 83, 85, 155, 2765, 3379, 3875, 5207, 10745, 15767, 31315, 40957, 45803, 46565, 51007, 80161 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (340*10^n - 43)/9 is prime.

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

Numbers corresponding to terms <= 5207 are certified primes.

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..19.

Patrick De Geest, PDP Reference Table - 373.

Makoto Kamada, Prime numbers of the form 377...773.

Index entries for primes involving repunits.

FORMULA

a(n) = A082708(n) - 2.

EXAMPLE

373 is prime, hence 1 is a term.

MATHEMATICA

Select[Range[0, 2000], PrimeQ[(340 10^# - 43) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)

PROG

(PARI) a=33; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+43)

(PARI) for(n=0, 1500, if(isprime((340*10^n-43)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A082708.

Sequence in context: A317467 A076163 A207977 * A141885 A262447 A165352

Adjacent sequences:  A056252 A056253 A056254 * A056256 A056257 A056258

KEYWORD

nonn,hard,more,changed

AUTHOR

Robert G. Wilson v, Aug 18 2000

EXTENSIONS

Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004

Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, Jun 15 2007

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

Two more terms from PDP table and a link added, and comments section updated, by Patrick De Geest, Nov 02 2014

Edited by Ray Chandler, Nov 05 2014

STATUS

approved

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Last modified September 25 21:12 EDT 2018. Contains 315425 sequences. (Running on oeis4.)