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A082704 Plateau and depression primes of the form (10^a(n)-1)/9+2*(10^[ a(n)-1 ]+1) or (28*10^[ a(n)-1 ]+17)/9. 2
3, 13, 15, 31, 105, 127, 343, 601, 9825 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Prime versus probable prime status and proofs are given in the author's table.

REFERENCES

C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.

LINKS

Table of n, a(n) for n=1..9.

Patrick De Geest, PDP Reference Table - 313.

Makoto Kamada, Prime numbers of the form 311...113.

Index entries for primes involving repunits.

FORMULA

a(n) = A056251(n) + 2.

EXAMPLE

a(n)=15 -> (10^15-1)/9+2*(10^14+1) = 311111111111113.

CROSSREFS

Cf. A082697-A082720, A056251, A068650.

Sequence in context: A113487 A032623 A146512 * A152270 A032919 A216044

Adjacent sequences:  A082701 A082702 A082703 * A082705 A082706 A082707

KEYWORD

nonn

AUTHOR

Patrick De Geest, Apr 13 2003.

EXTENSIONS

Edited by Ray Chandler, Nov 04 2014

STATUS

approved

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Last modified October 16 10:55 EDT 2019. Contains 328056 sequences. (Running on oeis4.)