What is the formula to calculate any given consecutive even numbers like 28 30 32 34 etc or 14 16 18 20 etc instead of adding them separately?

depends what you mean by a number ! I am going to assume you are talking about the real numbers (1,2,3,4,5 etc.)

You could formulate a series equation to give you only values of x = even number say you had 28+30+32+34+36+38= x instead of going through and adding them is there a formula to take like the first and last number to get the sum of all those numbers? I don't know if this really will work with all of them, but I came up with taking the first number plus the last number multiplied by half of the numbers you're adding together.