3744216domain: NAppears in sequencesa(n) = larger member of n-th pair of distinct, positive, triangular numbers whose sum and difference are also triangular numbers.at n=29A185128Triangular numbers, T(m), that are four-fifths of another triangular number: T(m) such that 5*T(m) = 4*T(k) for some k.at n=3A201003