Sum of first N natural numbers??

Sum of first 20 natural numbers is 410.

Find the sum of first 10 natural numbers

If S_1, S_2, S_3 are the sums of first n natural numbers, their squares and cubes respectively, show that 9S_2^ 2=S_3(1+8S_1)dot

Statement 1: The variance of first n even natural numbers is (n^2-1)/4 Statement 2: The sum of first n natural numbers is (n(n+1)/2 and the sum of squares of first n natural numbers is (n(n+1)(2n+1)/6 (1) Statement1 is true, Statement2 is true, Statement2 is a correct explanation for statement1 (2) Statement1 is true, Statement2 is true; Statement2 is not a correct explanation for statement1. (3) Statement1 is true, statement2 is false. (4) Statement1 is false, Statement2 is true

If S_(1), S_(2) and S_(3) are the sums of first n natureal numbers, their squares and their cubes respectively, then (S_(1)^(4)S_(2)^(2)-S_(2)^(2)S_(3)^(2))/(S_(1)^(2) +S_(2)^(2))=

The sum of first 10 natural numbers.

Find sum of first 50 natural numbers.

Find the sum of first 25 natural numbers.

If S_(1),S_(2),S_(3) are the sums of first n natural numbers,their squares and their cubes respectively then S_(3)(1+8S_(1))=

Find sum of first 1000 natural numbers.