A051239 Number of ways to arrange integers 1 through n so that the sum of each adjacent pair is prime, not counting reversals.

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

Offset

1,4

Comments

Similar to A036440, but not requiring 1 to be first and n to be last.

Links

Table of n, a(n) for n=1..28.

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

Jud McCranie

Extensions

More terms from Max Alekseyev, Jan 04 2008

a(25)-a(28) from Giovanni Resta, Apr 01 2014

Status

approved