106289domain: NAppears in sequencesa(n) = (4 + (-9)^n)/5.at n=6A083294Number of set partitions of [n] having the maximal possible number of pairs (m,m+1) such that m+1 is in some block b and m is in block b+1.at n=57A270967a(n) = Sum_{d|n} phi(d)^4.at n=26A342470