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A077791 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)/9+7*10^[ a(n)/2 ]. 1
3, 9, 13, 15, 769, 1333, 1351, 6331 (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..8.

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

Makoto Kamada, Prime numbers of the form 11...11811...11

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A107648(n)+1.

EXAMPLE

a(n)=13 -> (10^13-1)/9+7*10^6 = 1111118111111.

MATHEMATICA

Do[ If[ PrimeQ[(10^n + 63*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 6400, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

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

Sequence in context: A111230 A046865 A063791 * A176393 A239320 A243656

Adjacent sequences:  A077788 A077789 A077790 * A077792 A077793 A077794

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

STATUS

approved

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Last modified September 1 10:23 EDT 2015. Contains 261265 sequences.