- #1

- 601

- 4

1. This one is common: Sum of all integers 1+2+3+...=0.5(n^2 + n)

2. Sum of odd integers: 1+3+5+7+9......= n^2

3. Sum of even integers: 2+4+6+8.....= n^2 + n eg: Sum of first two: 2+4= 2^2 +2 =6

4. Sum of gap odd integers(odd integers with one gap) : 1+5+9+13+17....= (n+1)(n+2) eg. 1+5=(1+1)(1+2)=6

5.a. Sum of gap even integers: 2+6+10+14....= 2n^2 eg 2+6+10= 2(3)^2=18

5.b. Sum of gap even integers: 4+8+12+16...= 4(1+2+3+4+...) eg:4+8+12= 4(1+2+3)= 24