A210685 a(1)=-1, a(2)=2, thereafter a(n) = (1/(2n))*((7n-22)a(n-1)+2(2n-1)a(n-2)).

-1, 2, -2, 2, -1, 2, 2, 8, 22, 68, 212, 678, 2207, 7298, 24458, 82928, 284066, 981884, 3421316, 12007556, 42416486, 150718772, 538421588, 1932856592, 6969847484, 25237057112, 91729488352, 334589415278, 1224445617887, 4494622119426, 16545704494682, 61071167108960, 225982053183050

Offset

1,2

References

Liu Yanpei, On the number of rooted c-nets, J. Combin. Theory, B 36 (1984), 118-123. See the sequence R_n.

Links

Table of n, a(n) for n=1..33.

Formula

A000287(n) = (-1)^n*2 + a(n-1).

Maple

R:=proc(n) option remember; if n=1 then -1 elif n=2 then 2 else
(1/(2*n))*((7*n-22)*R(n-1)+2*(2*n-1)*R(n-2)); fi; end;
[seq(R(n), n=1..40)];

Mathematica

a[n_] := a[n] = Which[n == 1, -1, n == 2, 2, True, (1/(2*n))*((7*n-22)*a[n-1]+2*(2*n-1)*a[n-2])]; Table[a[n], {n, 1, 40}] (* Jean-François Alcover, Mar 06 2014, after Maple *)

Crossrefs

Cf. A000287.

Sequence in context: A366693 A147680 A192895 * A264051 A120965 A151931

Adjacent sequences: A210682 A210683 A210684 * A210686 A210687 A210688

Keyword

sign

Author

N. J. A. Sloane, Mar 28 2012

Status

approved