OFFSET
0,3
COMMENTS
The sequence a(n)=b(n)*(b(n)-1)/2 gives an SO(2),SO(5),SO(10),SO(20), ...
LINKS
FORMULA
a(n)=5*2^(-5+n)*(-4+5*2^n) for n>1. a(n)=6*a(n-1)-8*a(n-2) for n>3. G.f.: x*(1+4*x-7*x^2)/((1-2*x)*(1-4*x)). [Colin Barker, Aug 16 2012]
MATHEMATICA
Clear[a] a[0] = 1; a[1] = 2; a[2] = 5; a[n_] := a[n] = a[1]*a[n - 1]; Table[a[n]*(a[n] - 1)/2, {n, 0, 20}]
Join[{0, 1}, LinearRecurrence[{6, -8}, {10, 45}, 30]] (* Harvey P. Dale, May 23 2013 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Roger L. Bagula, Aug 10 2008
EXTENSIONS
Edited by N. J. A. Sloane, Aug 16 2008
Corrected the definition, which was describing an auxiliary sequence. - R. J. Mathar, Oct 29 2008
More terms from Harvey P. Dale, May 23 2013
STATUS
approved