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 A051239 Number of ways to arrange integers 1 through n so that the sum of each adjacent pair is prime, not counting reversals. 8
 1, 1, 1, 4, 2, 8, 12, 30, 70, 664, 1072, 8768, 11648, 37108, 95772, 1059816, 2047488, 12111712, 22802028, 120779959, 337801784, 4361743860, 11425028900, 142573286216, 429917269469, 4138239848098, 16171519847028, 214845911686065 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS Similar to A036440, but not requiring 1 to be first and n to be last. LINKS FORMULA For n>1, a(n) = A103839(n)/2. EXAMPLE 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. CROSSREFS Cf. A036440, A051237. Sequence in context: A321119 A246202 A134042 * A064821 A002291 A225872 Adjacent sequences:  A051236 A051237 A051238 * A051240 A051241 A051242 KEYWORD nonn,nice AUTHOR EXTENSIONS More terms from Max Alekseyev, Jan 04 2008 a(25)-a(28) from Giovanni Resta, Apr 01 2014 STATUS approved

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Last modified September 21 04:58 EDT 2020. Contains 337267 sequences. (Running on oeis4.)