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 A077789 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)/9+6*10^[ a(n)/2 ]. 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 Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's) Makoto Kamada, Prime numbers of the form 11...11711...11 FORMULA a(n) = 2*A107127(n)+1. EXAMPLE a(n)=7 -> (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 STATUS approved

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