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 A077778 Numbers k such that (10^k - 1) - 7*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime). 2
 3, 17, 19, 705, 1061, 1395, 2631, 3837, 5749, 11753, 13537, 125877, 269479 (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. REFERENCES C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9. LINKS Table of n, a(n) for n=1..13. Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's) Makoto Kamada, Prime numbers of the form 99...99299...99 Index entries for primes involving repunits. FORMULA a(n) = 2*A115073(n) + 1. EXAMPLE 17 is a term because (10^17 - 1) - 7*10^8 = 99999999299999999. MATHEMATICA Do[ If[ PrimeQ[10^n - 7*10^Floor[n/2] - 1], Print[n]], {n, 3, 14600, 2}] (* Robert G. Wilson v, Dec 16 2005 *) CROSSREFS Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187. Sequence in context: A177208 A370106 A147845 * A273420 A022127 A273448 Adjacent sequences: A077775 A077776 A077777 * A077779 A077780 A077781 KEYWORD more,nonn,base AUTHOR Patrick De Geest, Nov 16 2002 EXTENSIONS Two more terms from PWP table added by Patrick De Geest, Nov 05 2014 Name corrected by Jon E. Schoenfield, Oct 31 2018 STATUS approved

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Last modified April 13 18:46 EDT 2024. Contains 371644 sequences. (Running on oeis4.)