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a(n) = A046673(n)/2.
3

%I #12 Mar 08 2020 04:14:47

%S 1,18,660,42000,4142880,586776960,113020427520,28432576972800,

%T 9056055981772800,3562946373482496000,1697172166720622592000,

%U 962691052768668647424000,641260394342965606809600000,495681727573700350908825600000,440084864982859007245221888000000

%N a(n) = A046673(n)/2.

%Y Cf. A000254, A049034, A046673.

%K nonn

%O 1,2

%A _N. J. A. Sloane_

%E Offset changed to 1 by _Jon E. Schoenfield_, Mar 08 2020