数列an满足Sn+Sn+1=5/3an+1,a1=a,求an.题中n+1均为角标,

s(n) + s(n+1) = (5/3)a(n+1) = (5/3)[s(n+1)-s(n)],
s(n+1) = 4s(n),
{s(n)}是首项为s(1)=a(1)=a,公比为4的等比数列.
s(n) = a*4^(n-1).
a(n+1) = (3/5)[s(n) + s(n+1)] = (3/5)[a*4^(n-1) + a*4^n] = 3a*4^(n-1) = 3a*4^(n+1-2).
{a(n)}通项公式为,
a(1)=a,
n>=2时,a(n) = 3a*4^(n-2)