If a sequence is 1,3,6,10,15,21 ··· n, then the formula of the first n sum of the sequence is many?

Add up

RELATED INFORMATIONS

1. 2N-1 of the N-1 power of 2 leads to the sum of the first n terms of the formula
2. For real number x, use [x] to represent the largest integer not exceeding x, such as [0.32] = 0, [5.68] = 5. If n is a positive integer, an = [N4], and Sn is the sum of the first n terms of the sequence {an}, then S8=______ 、S4n=______ ．
3. Sum: S = 1 + 2x + 3x ^ 2 +... + NX ^ (n-1)
4. Sum of sequence: 1 * 3 + 3 * 5 + 5 * 7 +. + (2n-1) (2n + 1)
5. Sequence summation 1 + 3 + 5 +. + (2n-1)
6. Can (n + 7) 2 - (N-5) 2 be divisible by 24 when n is a natural number? Give reasons
7. As shown in the figure, ab = AC, ad = AE, ∠ BAC = ∠ DAE
8. As shown in the figure, in △ ABC, ab = AC, ad is high, and am is the bisector of ∠ CAE at the outer angle of △ ABC. (1) draw the bisector DN of ∠ ADC with ruler; (2) let DN and am intersect at point F to judge the shape of △ ADF. (only write the result)
9. If the degree ratio of the top and bottom angles of an isosceles triangle is 2:1, what are the top and bottom angles of the triangle
10. An isosceles triangle, the ratio of its vertex angle to its base angle is 1:4, and its base angle is ()?
11. What is the 20th of sequence 1,3,6,10,15,21 ··
12. Sequence summation 1 / 3 + 1 / 5 + 1 / 7 + +1/21=?
13. Sequence 0 + 1 + 3 + 6 + 10 What is the summation formula?
14. [sequence summation] 1 + 2x + 3x ^ 2 + +nx^n-1=()? 1+2*x+3*(x^2)+…… +n*x^(n-1)=( When x is not equal to 1, = (1-x ^ n) / [(1-x) ^ 2] - [n * (x ^ n)] / (1-x) When x equals 1, = n (n + x) / 2
15. It is known that the sum of the first n terms of the sequence {an} is Sn, A1 = 1, an + 1 = 2Sn + 1, (n belongs to n *), and BN & gt; 0 (n) in the arithmetic sequence {BN} It is known that the sum of the first n terms of the sequence {an} is Sn, A1 = 1, an + 1 = 2Sn + 1, (n belongs to n *), BN > 0 (n belongs to n *) in the arithmetic sequence {BN}, and B1 + B2 + B3 = 15, and a1 + B1, A2 + B2, A3 + B3 are equally proportional. 1) find the general term formula of the sequence {an}, {BN}, 2), find the first n terms and TN of the sequence {an · BN}
16. If BN = | an | (n ∈ n), find the first n terms and TN of {BN}
17. Given the N-1 degree of sequence an = 2n + 1 bn = 8. CN = an * BN. Find the first n terms of CN and TN
18. Note CN = an × BN to find the first n terms and TN of sequence {CN} an=2n-1 bn=2/(3^n)
19. Given the sequence an = 4n-2 and BN = 2 / 4 ^ (n-1), let CN = an / BN, find the first n terms and TN of the sequence {CN}
20. If an > 0, A1 = 1, an ^ 2 - (an-1) ^ 2 = (an-1) * an, If an > 0, A1 = 1, an ^ 2 - (an-1) ^ 2 = (an-1) * an, then 1 / (a1 + A2) + 1 / (A2 + a3) + +1/(an-1+an) =