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A077789 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)/9+6*10^[ a(n)/2 ]. 2
7, 67, 623, 5867, 44471, 78331, 83171 (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.

a(8) > 10^5. - Robert Price, Apr 30 2017

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 11...11711...11

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A107127(n)+1.

EXAMPLE

a(n)=7 -> (10^7-1)/9+6*10^3 = 1117111.

MATHEMATICA

Do[ If[ PrimeQ[(10^n + 54*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 6000, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

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

Sequence in context: A250227 A250275 A240373 * A250165 A186655 A253175

Adjacent sequences:  A077786 A077787 A077788 * A077790 A077791 A077792

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

EXTENSIONS

a(5)-a(7) from Robert Price, Apr 30 2017

STATUS

approved

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Last modified September 23 21:14 EDT 2017. Contains 292391 sequences.