2f(n+1)=2f(n)+n
2f(n+2)=2f(n+1)+n+1=2f(n)+n+n+1
.
2f(n+k)=2f(n)+k*n+(1+2+..+k-1)
2f(1+k)=2f(1)+k+1+2+...+k-1
=2f(1)+k*(k+1)/2
2f(2007)=2*2+2006*2007/2=2013025
f(2007)= 1006512.5
2f(n+1)=2f(n)+n
2f(n+2)=2f(n+1)+n+1=2f(n)+n+n+1
.
2f(n+k)=2f(n)+k*n+(1+2+..+k-1)
2f(1+k)=2f(1)+k+1+2+...+k-1
=2f(1)+k*(k+1)/2
2f(2007)=2*2+2006*2007/2=2013025
f(2007)= 1006512.5