The {{MATH_10}} (sigma) indicates that a sum is being taken. The variable {{MATH_11}} is called the {{CMD_12}}index{{CMD_13}} of the sum. The numbers at the top and bottom of the {{MATH_14}} are called the {{CMD_15}}upper and lower limits{{CMD_16}} of the summation. In this case, the upper limit is {{MATH_17}}, and the lower limit is {{MATH_18}}. The notation means that we will take every integer value of {{MATH_19}} between {{MATH_20}} and {{MATH_21}} (so {{MATH_22}}, {{MATH_23}}, {{MATH_24}}, {{MATH_25}}, and {{MATH_26}}) and plug them each into the summand formula (here that formula is {{MATH_27}}). Then those are all added together. {{MATH_28}}