Sequence and formula 3. Sequence 1,3,7,12,21 ,n ,…… What is the nth number of? 4. Sequence 3 ^ root 2 + 1, - 3, 3 ^ root 2-1, - 3 ^ 3-2 root 2 What's a formula for?

Sequence and formula 3. Sequence 1,3,7,12,21 ,n ,…… What is the nth number of? 4. Sequence 3 ^ root 2 + 1, - 3, 3 ^ root 2-1, - 3 ^ 3-2 root 2 What's a formula for?

1:(n+0^2-n^2

Find Sn = the square of one plus the square of two plus the square of three all the way up to n
There's a formula. Forget it

Sn=n(n+1)(2n+1)/6

On all the relevant formulas of high school mathematics "sequence"
Formula of sequence

Equal ratio sequence: if q = 1, then s = n * A1, if Q ≠ 1, s = a1 + A1 * q + A1 * q ^ 2 + +A1 * q ^ (n-1) multiply both sides of the equation Q s * q = A1 * q + A1 * q ^ 2 + A1 * q ^ 3 + +Formula A1 * q ^ 1-2 has s = A1 * (1-Q ^ n) / (1-Q) arithmetic sequence s = a1 + (a1 + D) + (a1 + 2D) + (a1 + (n-1) * d) put this