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A077779
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Numbers k such that (10^k - 1)/9 + 2*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime).
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3
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OFFSET
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1,1
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COMMENTS
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Prime versus probable prime status and proofs are given in the author's table.
The number k = 1 would also correspond to a prime, 3, but not "near-repdigit" or "wing" in a strict sense. - M. F. Hasler, Feb 09 2020
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REFERENCES
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C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
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LINKS
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FORMULA
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EXAMPLE
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5 is a term because (10^5 - 1)/9 + 2*10^2 = 11311.
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MATHEMATICA
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Do[ If[ PrimeQ[(10^n + 18*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 20000, 2}] (* Robert G. Wilson v, Dec 16 2005 *)
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CROSSREFS
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See A332113 for the (prime and composite) near-repunit palindromes 1..131..1.
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KEYWORD
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nonn,base,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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