JSFiddle - React, Tailwind, and code Playground

JavaScript

const MAX = 30;
const usedNumbers = [3, 4, 12, 13, 14, 16, 23, 27];

// https://stackoverflow.com/questions/3746725/how-to-create-an-array-containing-1-n
const notUsedNumbers = Array.from(Array(MAX), (_, i) => i+1).filter(i => !usedNumbers.includes(i));

console.log(notUsedNumbers);