Dynkin type D7—grassmannian.info
Dynkin type $\mathrm{ D }_{ 7 }$
«$\mathrm{ D }_{ 6 }$
$\mathrm{ D }_{ 8 }$»
$2n-2=12$
$2n^2-n=91$
$1,3,5,\ldots,2n-3,n-1=1,3,5,6,7,9,11$
$\mathrm{S}_{ 7 }\rtimes(\mathbb{Z}/2\mathbb{Z})^{\oplus 6 }$
$n!2^{n-1}=7!2^{ 6 }=322560$
$2n(n-1)=84$
\begin{pmatrix} 2 & -1 & 0 & 0 & 0 & 0 & 0 \\ -1 & 2 & -1 & 0 & 0 & 0 & 0 \\ 0 & -1 & 2 & -1 & 0 & 0 & 0 \\ 0 & 0 & -1 & 2 & -1 & 0 & 0 \\ 0 & 0 & 0 & -1 & 2 & -1 & -1 \\ 0 & 0 & 0 & 0 & -1 & 2 & 0 \\ 0 & 0 & 0 & 0 & -1 & 0 & 2 \\ \end{pmatrix}