
展开全部
a1=1,a(n+1)=an+n
a100=a99+99
=a98+98+99
=a97+97+98+99
=…
=ak+k+(k+1)+(k+2)+…+99
=…
=a1+1+2+3+…+99
=1+(1+99)×99/2
=1+4950
=4951
a100=a99+99
=a98+98+99
=a97+97+98+99
=…
=ak+k+(k+1)+(k+2)+…+99
=…
=a1+1+2+3+…+99
=1+(1+99)×99/2
=1+4950
=4951
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