69377domain: NAppears in sequencesa(n) = A216960(n)/2.at n=36A216961Number of (n+2) X 7 0..1 matrices with each 3 X 3 subblock idempotent.at n=18A224556a(n)/A002939(n+1) is the Kirchhoff index of the disjoint union of two complete graphs each on n and n+1 vertices with the empty graph on n+1 vertices.at n=15A338588