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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
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.
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 *)
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