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 A077783 Numbers k such that (10^k-1)/9 + 4*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime). 1
 3, 15, 91, 231, 1363, 2497, 4963, 5379, 12397, 26395, 120253 (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(12) > 2*10^5. - Robert Price, 12 Oct 2015 REFERENCES C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9. LINKS Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's) Makoto Kamada, Prime numbers of the form 11...11511...11 FORMULA a(n) = 2*A107125(n) + 1. EXAMPLE a(n) = 15 -> (10^15 - 1)/9 + 4*10^7 = 111111151111111. MATHEMATICA Do[ If[ PrimeQ[(10^n + 36*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 26400, 2}] (* Robert G. Wilson v, Dec 16 2005 *) PROG (MAGMA) [n: n in [3..2000 by 2] | IsPrime((10^n+36*10^(n div 2)-1) div 9)]; // Vincenzo Librandi, Oct 13 2015 CROSSREFS Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187. Sequence in context: A024339 A319950 A034954 * A047019 A099251 A171790 Adjacent sequences:  A077780 A077781 A077782 * A077784 A077785 A077786 KEYWORD more,nonn,base,changed AUTHOR Patrick De Geest, Nov 16 2002 EXTENSIONS a(11) from Robert Price, Oct 12 2015 Name edited by Jon E. Schoenfield, Oct 13 2015 STATUS approved

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Last modified November 14 06:14 EST 2018. Contains 317162 sequences. (Running on oeis4.)