16687440domain: NAppears in sequencesk-imperfect numbers for some k >= 1.at n=27A1277243-imperfect numbers.at n=19A127726Triangular array read by rows. T(n,k) is the number of sets of lists (as in A000262(n)) with exactly k size 2 lists, n >= 0, 0 <= k <= floor(n/2).at n=39A351823