求数列2,7,16,30,50.的通式

1个回答

  • 2=1+2-1

    7=(1+2)+(1+2+3)-2

    16=(1+2)+(1+2+3)+(1+2+3+4)-3

    30=

    (1+2)+(1+2+3)+(1+2+3+4)+(1+2+3+4+5)-4

    50=

    (1+2)+(1+2+3)+(1+2+3+4)+(1+2+3+4+5)+(1+2+3+4+5+6)-5

    则第n项为数列a(n)=(n+1)n/2前n+1项之和-n-1.即[(n+1)*(n+2)*(2n+6)/12]-n-1