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数列{an}满足递推式an=3an-1+3n-1(n≥2),且a1=5.
(Ⅰ)求a2,a3的值;
(Ⅱ)若存在实数λ使为等差数列,求λ的值及{an}的通项公式;
(Ⅲ)求{an}的前n项和Sn.
数列{an}满足递推式an=3an-1+3n-1(n≥2),又a1=5,则使得{}为等差数列的实数λ=________