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A077790 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)/3+4*10^[ a(n)/2 ]. 1
3, 7, 15, 23, 27, 35, 59, 63, 67, 155, 1867, 3111, 23517 (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(14) > 200,000. - Robert Price, Dec 29 2016

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..13.

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

Makoto Kamada, Prime numbers of the form 33...33733...33

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A183176(n)+1.

EXAMPLE

a(n)=23 -> (10^23-1)/3+4*10^11 = 33333333333733333333333.

MATHEMATICA

Do[ If[ PrimeQ[(10^n + 12*10^Floor[n/2] - 1)/3], Print[n]], {n, 3, 23600, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

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

Sequence in context: A229527 A091711 A103007 * A165469 A160160 A192122

Adjacent sequences:  A077787 A077788 A077789 * A077791 A077792 A077793

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

STATUS

approved

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Last modified September 23 21:15 EDT 2017. Contains 292391 sequences.