Search: id:A051239
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%I A051239
%S A051239 1,1,1,4,2,8,12,30,70,664,1072,8768,11648,37108,95772,1059816,2047488,
%T A051239 12111712,22802028,120779959,337801784,4361743860,11425028900,142573286216
%N A051239 Number of ways to arrange integers 1 through n so that the sum of each 
               adjacent pair is prime, not counting reversals.
%C A051239 Similar to A036440, but not requiring 1 to be first and n to be last.
%F A051239 For n>1, A051239(n)=A103839(n)/2.
%e A051239 a(5)=2 since 1,4,3,2,5 and 3,4,1,2,5 have the property that the sum of 
               each adjacent pair is prime.
%Y A051239 Cf. A036440, A051237.
%Y A051239 Sequence in context: A050128 A134042 A064821 this_sequence A002291 A110622 
               A130078
%Y A051239 Adjacent sequences: A051236 A051237 A051238 this_sequence A051240 A051241 
               A051242
%K A051239 nonn,nice
%O A051239 1,4
%A A051239 Jud McCranie (j.mccranie(AT)comcast.net)
%E A051239 More terms from Max Alekseyev, Jan 04 2008

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