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A077792
Numbers k such that (10^k - 1)/3 + 5*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime).
2
3, 15, 171, 189, 547, 713, 2155, 3595, 13517, 60465
OFFSET
1,1
COMMENTS
Prime versus probable prime status and proofs are given in the author's table.
a(11) > 2*10^5. - Robert Price, Apr 21 2016
REFERENCES
C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
FORMULA
a(n) = 2*A183177(n) + 1.
EXAMPLE
15 is a term because (10^15 - 1)/3 + 5*10^7 = 333333383333333.
MATHEMATICA
Do[ If[ PrimeQ[(10^n + 15*10^Floor[n/2] - 1)/3], Print[n]], {n, 3, 13600, 2}] (* Robert G. Wilson v, Dec 16 2005 *)
KEYWORD
more,nonn,base
AUTHOR
Patrick De Geest, Nov 16 2002
EXTENSIONS
a(10) from Robert Price, Apr 21 2016
Name corrected by Jon E. Schoenfield, Oct 31 2018
STATUS
approved