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A077789 Numbers k such that (10^k - 1)/9 + 6*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime). 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

7 is a term because (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

Name corrected by Jon E. Schoenfield, Oct 31 2018

STATUS

approved

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Last modified October 21 21:51 EDT 2021. Contains 348155 sequences. (Running on oeis4.)