27557748813domain: NAppears in sequencesa(n) = 7*a(n-1) - 14*a(n-2) + 7*a(n-3) with a(1)=7, a(2)=21, a(3)=70.at n=17A215494Sum of n-th powers of the roots of x^3 + 7*x^2 + 14*x + 7.at n=18A322459