数列满足1/3a1+1/3方a2+1/3三次方a3+.+1/3n次方（3的n次方）=3n+1,则an=

Question

数列满足1/3a1+1/3方a2+1/3三次方a3+.+1/3n次方（3的n次方）=3n+1,则an=

Answer 1

n=1 1/3a1=4 a1=12
n>1 1/3^n an=3n+1-3(n-1)-1=3 即an=3 * 3^n(n>=2)