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A051239
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Number of ways to arrange integers 1 through n so that the sum of each adjacent pair is prime, not counting reversals.
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7
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1, 1, 1, 4, 2, 8, 12, 30, 70, 664, 1072, 8768, 11648, 37108, 95772, 1059816, 2047488, 12111712, 22802028, 120779959, 337801784, 4361743860, 11425028900, 142573286216
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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COMMENTS
| Similar to A036440, but not requiring 1 to be first and n to be last.
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FORMULA
| For n>1, A051239(n)=A103839(n)/2.
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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.
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CROSSREFS
| Cf. A036440, A051237.
Sequence in context: A050128 A134042 * A064821 A002291 A110622 A130078
Adjacent sequences: A051236 A051237 A051238 * A051240 A051241 A051242
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KEYWORD
| nonn,nice
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AUTHOR
| Jud McCranie (JudMcCranie(AT)ugaalum.uga.edu)
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EXTENSIONS
| More terms from Max Alekseyev, Jan 04 2008
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