1. 
y2 := dsolve({D(D(y))(t) - y(t) = 0, y(0) = 1, D(y)(0) = 0}, numeric);
y2(1)[2];
                    y(t) = 1.54308053257804


y3 := dsolve({D(D(D(y)))(t) - y(t) = 0, y(0) = 1, D(y)(0) = 0, D(D(y))(0) = 0}, numeric);
y3(1)[2];
                    y(t) = 1.16805828131390


y4 := dsolve({D(D(D(D(y))))(t) - y(t) = 0, y(0) = 1, D(y)(0) = 0, D(D(y))(0) = 0, D(D(D(y)))(0) = 0}, numeric);
y4(1)[2];
                    y(t) = 1.04169144064877


y5 := dsolve({D(D(D(D(D(y)))))(t) - y(t) = 0, y(0) = 1, D(y)(0) = 0, D(D(y))(0) = 0, D(D(D(y)))(0) = 0, D(D(D(D(y))))(0) = 0}, numeric);
y5(1)[2];
                    y(t) = 1.00833368226938


y6 := dsolve({D(D(D(D(D(D(y))))))(t) - y(t) = 0, y(0) = 1, D(y)(0) = 0, D(D(y))(0) = 0, D(D(D(y)))(0) = 0, D(D(D(D(y))))(0) = 0, D(D(D(D(D(y)))))(0) = 0}, numeric);
y6(1)[2];
                    y(t) = 1.00138887678885


y7 := dsolve({D(D(D(D(D(D(D(y)))))))(t) - y(t) = 0, y(0) = 1, D(y)(0) = 0, D(D(y))(0) = 0, D(D(D(y)))(0) = 0, D(D(D(D(y))))(0) = 0, D(D(D(D(D(y)))))(0) = 0, D(D(D(D(D(D(y))))))(0) = 0}, numeric);
y7(1)[2];
                    y(t) = 1.00019839735008


y8 := dsolve({D(D(D(D(D(D(D(D(y))))))))(t) - y(t) = 0, y(0) = 1, D(y)(0) = 0, D(D(y))(0) = 0, D(D(D(y)))(0) = 0, D(D(D(D(y))))(0) = 0, D(D(D(D(D(y)))))(0) = 0, D(D(D(D(D(D(y))))))(0) = 0, D(D(D(D(D(D(D(y)))))))(0) = 0}, numeric);
y8(1)[2];
                    y(t) = 1.00002479421227


y9 := dsolve({D(D(D(D(D(D(D(D(D(y)))))))))(t) - y(t) = 0, y(0) = 1, D(y)(0) = 0, D(D(y))(0) = 0, D(D(D(y)))(0) = 0, D(D(D(D(y))))(0) = 0, D(D(D(D(D(y)))))(0) = 0, D(D(D(D(D(D(y))))))(0) = 0, D(D(D(D(D(D(D(y)))))))(0) = 0, D(D(D(D(D(D(D(D(y))))))))(0) = 0}, numeric);
y9(1)[2];
                    y(t) = 1.00000275343299


y10 := dsolve({D(D(D(D(D(D(D(D(D(D(y))))))))))(t) - y(t) = 0, y(0) = 1, D(y)(0) = 0, D(D(y))(0) = 0, D(D(D(y)))(0) = 0, D(D(D(D(y))))(0) = 0, D(D(D(D(D(y)))))(0) = 0, D(D(D(D(D(D(y))))))(0) = 0, D(D(D(D(D(D(D(y)))))))(0) = 0, D(D(D(D(D(D(D(D(y))))))))(0) = 0, D(D(D(D(D(D(D(D(D(y)))))))))(0) = 0}, numeric);
y10(1)[2];
                    y(t) = 1.00000027504110
3. 
rsolve({a(n) - 3*a(n - 1) + 2*a(n - 2) = 0, a(0) = 2, a(1) = 3}, a(n));
                             2n  + 1
4.
rsolve({a(n) - a(n - 4) = 0, a(0) = 1, a(1) = 0, a(2) = 0, a(3) = 0}, a(n));
                  ¼ + (-i)n/4 + in/4 + (-1)n/4