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A056247 Indices of primes in sequence defined by A(0) = 11, A(n) = 10*A(n-1) + 51 for n > 0. 2
0, 3, 11, 15, 17, 35, 51, 71, 99, 6231, 24027, 40221, 66393 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (150*10^n - 51)/9 is prime.

Numbers n such that digit 1 followed by n >= 0 occurrences of digit 6 followed by digit 1 is prime.

Numbers corresponding to terms <= 99 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..13.

Patrick De Geest, PDP Reference Table - 161.

Makoto Kamada, Prime numbers of the form 166...661.

Index entries for primes involving repunits.

FORMULA

a(n) = A082700(n-1) - 2 for n > 1.

EXAMPLE

16661 is prime, hence 3 is a term.

MATHEMATICA

Select[Range[0, 2000], PrimeQ[(150 10^# - 51) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)

PROG

(PARI) a=11; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+51)

(PARI) for(n=0, 1500, if(isprime((150*10^n-51)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A068647, A082700.

Sequence in context: A134629 A245522 A030715 * A039275 A044971 A106374

Adjacent sequences:  A056244 A056245 A056246 * A056248 A056249 A056250

KEYWORD

nonn,hard,more

AUTHOR

Robert G. Wilson v, Aug 18 2000

EXTENSIONS

Additional comments from Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004

Edited by N. J. A. Sloane, Jun 15 2007

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

Added one more term from the PDP table and a link, by Patrick De Geest, Nov 02 2014

Edited by Ray Chandler, Nov 04 2014

STATUS

approved

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Last modified September 25 11:05 EDT 2018. Contains 315389 sequences. (Running on oeis4.)