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A077782 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)-5*10^[ a(n)/2 ]. 1
29, 45, 73, 209, 2273, 35729, 50897 (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..7.

Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)

Makoto Kamada, Prime numbers of the form 99...99499...99

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A183185(n)+1.

EXAMPLE

a(n)=29 -> (10^29-1)-5*10^14 = 99999999999999499999999999999.

MATHEMATICA

Do[ If[ PrimeQ[10^n - 5*10^Floor[n/2] - 1], Print[n]], {n, 3, 50900, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.

Sequence in context: A020997 A108280 A248429 * A059414 A110054 A104912

Adjacent sequences:  A077779 A077780 A077781 * A077783 A077784 A077785

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

STATUS

approved

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Last modified September 23 21:16 EDT 2017. Contains 292391 sequences.