32793751175domain: NAppears in sequencesa(n) = 7^(floor(n/3))*A(n), where A(n) = A(n-1) + A(n-2) + A(n-3)/7, with A(0)=3, A(1)=1, A(2)=3.at n=21A215828Sum of n-th powers of the roots of x^3 -31* x^2 - 25*x - 1.at n=7A274592