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A077780 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)/9 + 3*10^[ a(n)/2 ]. 1
5, 7, 65, 91, 3089 (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..5.

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

Makoto Kamada, Prime numbers of the form 11...11411...11

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A107124(n)+1.

EXAMPLE

a(n)=7 -> (10^7-1)/9+3*10^3 = 1114111.

MATHEMATICA

Do[ If[ PrimeQ[(10^n + 27*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 3100, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

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

Sequence in context: A201109 A177336 A108200 * A260829 A130189 A180755

Adjacent sequences:  A077777 A077778 A077779 * A077781 A077782 A077783

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

STATUS

approved

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Last modified September 23 20:33 EDT 2017. Contains 292391 sequences.