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A039944 Undulating palindromic primes of form ABABAB...BA with alternating prime and nonprime digits.

%I A039944 #20 Jul 22 2022 17:46:30
%S A039944 2,3,5,7,131,151,313,383,787,797,929,74747,78787,95959,1212121,
%T A039944 383838383,929292929,979797979,12121212121,151515151515151,
%U A039944 383838383838383,38383838383838383,74747474747474747,95959595959595959,383838383838383838383,787878787878787878787
%N A039944 Undulating palindromic primes of form ABABAB...BA with alternating prime and nonprime digits.
%C A039944 There are 52 terms of integer length 999 or less. The first term with integer length greater than 999 has 1295 digits and is 9595...5959. - _Harvey P. Dale_, Jul 12 2018
%D A039944 C. A. Pickover, "Wonders of Numbers", Oxford New York 2001, Chapter 52, pp. 123-124, 316-317.
%H A039944 Harvey P. Dale, <a href="/A039944/b039944.txt">Table of n, a(n) for n = 1..52</a>
%H A039944 C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," <a href="http://www.zentralblatt-math.org/zmath/en/search/?q=an:0983.00008&amp;format=complete">Zentralblatt review</a>
%t A039944 f[x_]:=Module[{pr,cm},pr=Select[Flatten[Table[FromDigits[PadRight[{},x,{a,b}]],{a,{3,7}},{b,{1,4,6,8,9}}]],PrimeQ];cm=Select[ Flatten[ Table[ FromDigits[PadRight[{},x,{a,b}]],{a,{1,9}},{b,{2,3,5,7}}]],PrimeQ]; Sort[ Join[pr,cm]]]; Join[{2,3,5,7},Flatten[ Table[ f[x],{x,3,999,2}]]]//Union (* _Harvey P. Dale_, Jul 12 2018 *)
%K A039944 base,nonn
%O A039944 1,1
%A A039944 _G. L. Honaker, Jr._
%E A039944 More terms from _Harvey P. Dale_, Jul 12 2018