已知数列An满足A1=1,A2=2,An+2=(1+cos*2 nπ/2)+sin2* nπ/2,则该数列的前20项的和为?已知数列An满足A1=1,A2=2,An+2=(1+cos*2nπ/2)+sin2*nπ/2,则该数列的前20项的和为?

已知数列an满足an=1+2+...+n,且1/a1+1/a2+...+1/an 已知数列{an}满足a1=1,a2=3,an+2=3an+1-2an求an 数列{An}满足a1=1/2,a1+a2+..+an=n方an,求an 已知数列an'满足a1=1/2,a1+a2+a3+...+an=n^2an,求通项公式 已知数列an满足a1=0 a2=1 an=(An-1+An-2)/2 求liman 已知数列an满足a1=0 a2=1 an=(An-1+An-2)/2 求liman 几个数列问题.已知数列{an} a1=1,an+1=an/(1+n^2*an) 求an 已知数列{an} 满足a1=1 a1*a2*a3.*an=n^2 求an 已知数列满足a1=1/2,an+1=2an/(an+1),求a1,a2已知数列满足a1=1/2,a(n+1)=2an/(an+1),求a1,a2;证明0 已知数列{an}满足：a1+a2+a3+.+an=n^2,求数列{an}的通项an. 已知递增数列{an}满足a1=1,(2an+1)=an+(an+2),且a1,a2,a4成等比数列.求an 关于数列极限的已知数列an满足a1=0 a2=1 an=(an-1+an-2)/2 求lim(n->无穷）an 已知数列{an}满足:a1=1,且an-an-1=2n,求(1)a2,a3,a4.(2)求数列{an}的通项an 已知数列(an)满足a1=1,an+1=2an/an+2(n∈N*) 求a2,a3,a4,a5 猜想数列(an)的通项公 已知数列an满足an=1+2+...n,且（1/a1）+(1/a2）+...(1/an) 已知数列{an}满足a1+a2+...+an=n²an求其通项an 数列an满足a1=1/2,a1+a2+a3……an=n^2an,则an 已知数列{an}中满足a1=1,a(n+1)=2an+1 (n∈N*),证明a1/a2+a2/a3+…+an/a(n+1) 已知数列{an}满足关系式lg（1+a1+a2+.+an）=n,求数列{an}的通项公式