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A056262 Indices of primes in sequence defined by A(0) = 77, A(n) = 10*A(n-1) + 17 for n > 0. 1
1, 3, 85, 111, 169, 565, 1687, 8901, 115809 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (710*10^n - 17)/9 is prime.

Numbers n such that digit 7 followed by n >= 0 occurrences of digit 8 followed by digit 7 is prime.

Numbers corresponding to terms <= 1687 are certified primes. For larger numbers see P. De Geest, PDP Reference Table.

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..9.

Patrick De Geest, PDP Reference Table - 787.

Makoto Kamada, Prime numbers of the form 788...887.

Index entries for primes involving repunits.

FORMULA

a(n) = A082715(n) - 2.

EXAMPLE

787 is prime, hence 1 is a term.

PROG

(PARI) a=77; for(n=0, 1700, if(isprime(a), print1(n, ", ")); a=10*a+17)

(PARI) for(n=0, 1700, if(isprime((710*10^n-17)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A082715.

Sequence in context: A215911 A203510 A065162 * A042587 A156879 A120264

Adjacent sequences:  A056259 A056260 A056261 * A056263 A056264 A056265

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 03 2004

Edited by N. J. A. Sloane at the suggestion of Andrew Plewe, Jun 05 2007

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

One more term added from PDP table 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 July 20 11:55 EDT 2018. Contains 312804 sequences. (Running on oeis4.)