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A077775 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)/3 - 2*10^[ a(n)/2 ]. 46
3, 7, 15, 123, 181, 185, 539, 597, 643, 743, 1553, 3135, 4769, 5133, 6177, 11733, 16103, 18997, 25271, 49025, 65043, 87965 (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(23) > 2*10^5. - Robert Price, Jan 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..22.

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

Makoto Kamada, Prime numbers of the form 33...33133...33

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A183174(n)+1.

EXAMPLE

a(n)=15 -> (10^15-1)/3-2*10^7 = 333333313333333.

MATHEMATICA

Do[ If[ PrimeQ[(10^n - 6*10^Floor[n/2] - 1)/3], Print[n]], {n, 3, 49100, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

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

Sequence in context: A154795 A193831 A246719 * A197594 A206851 A033089

Adjacent sequences:  A077772 A077773 A077774 * A077776 A077777 A077778

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

EXTENSIONS

a(21)-a(22) from Robert Price, Jan 29 2016

a(21) corrected by Robert Price, Feb 03 2016

STATUS

approved

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