%I #44 Mar 26 2020 06:38:15
%S 5,7,13,47,73,139,1123,1447,6877,8209,18041,27955,39311,64801
%N Numbers k such that 7*(10^k - 1)/9 - 3*10^floor(k/2) is a palindromic wing prime (also known as near-repdigit palindromic prime).
%C Prime versus probable prime status and proofs are given in the author's table.
%C a(15) > 2*10^5. - _Robert Price_, Nov 23 2015
%D C. Caldwell and H. Dubner, The near repdigit primes A(n-k-1)B(1)A(k), especially 9(n-k-1)8(1)9(k), Journal of Recreational Mathematics, Volume 28, No. 1, 1996-97, pp. 1-9.
%H Patrick De Geest, World!Of Numbers, <a href="http://www.worldofnumbers.com/wing.htm#pwp747">Palindromic Wing Primes (PWP's)</a>
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/7/77477.htm#prime">Prime numbers of the form 77...77477...77</a>
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = 2*A183179(n) + 1.
%e 7 is a term because 7*(10^7 - 1)/9 - 3*10^3 = 7774777.
%t Do[ If[ PrimeQ[(7*10^n - 27*10^Floor[n/2] - 7)/9], Print[n]], {n, 3, 39400, 2}] (* _Robert G. Wilson v_, Dec 16 2005 *)
%o (PARI) for(n=1, 1e3, if(ispseudoprime((7*10^(2*n+1)-27*10^n-7)/9), print1(2*n+1, ", "))) \\ _Altug Alkan_, Nov 23 2015
%Y Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.
%K more,nonn,base
%O 1,1
%A _Patrick De Geest_, Nov 16 2002
%E a(14) from _Robert Price_, Nov 23 2015
%E Name corrected by _Jon E. Schoenfield_, Oct 31 2018
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