2-3-4

Do you mean one of these? Here are quick results for the common interpretations:

• If it’s the arithmetic expression 2 - 3 - 4 (left to right): (2 - 3) - 4 = -5.
• If it’s the sequence 2, 3, 4: it’s an arithmetic sequence with first term a1 = 2 and common difference d = 1. General term a_n = n + 1. Sum of the first n terms: S_n = n/2 * (2a1 + (n-1)d) = n/2 * (4 + n - 1) = n(n+3)/2. For the first 3 terms, S_3 = 9.
• If you meant the range from 2 to 4 inclusive: the numbers are 2, 3, 4 (same as above).

If you meant something else (e.g., 2^(-3) - 4, or a set notation), tell me and I’ll tailor the answer.