leve.js

var expNeeded = [
  0,
  300, 600, 1100, 1700, 2300,
  4200, 6000, 7350, 9930, 11800,
  15600, 19600, 23700, 26400, 30500,
  35400, 40500, 45700, 51000, 56600,
  63900, 71400, 79100, 87100, 95209,
  109800, 124800, 140200, 155900, 162500,
  175900, 189600, 203500, 217900, 232320,
  249900, 267800, 286200, 304900, 324000,
  340200, 356800, 373700, 390800, 408200,
  437600, 467500, 498000, 529000, 562000
];
 
var expTotal = [
  0,
  300, 900, 2000, 3700, 6000,
  10200, 16200, 23550, 33480, 45280,
  60880, 80480, 104180, 130580, 161080,
  196480, 236980, 282680, 333680, 390280,
  454180, 525580, 604680, 691780, 786989,
  896789, 1021589, 1161789, 1317689, 1480189,
  1656089, 1845689, 2049189, 2267089, 2499409,
  2749309, 3017109, 3303309, 3608209, 3932209,
  4272409, 4629209, 5002909, 5393709, 5801909,
  6239509, 6707009, 7205009, 7734009, 8296009
];

function calculateExp(level, exp) {
  return expTotal[level - 1] + exp
}
 
function calculateLevel(exp) {
  for(var i = expTotal.length; i >= 0; i--) {
    if(expTotal[i] <= exp) {
      return i + 1;
    }
  }
  return 0;
}

function calculateBestLeve(leves, exp) {
  var level = calculateLevel(exp);
  return leves.sort(function(a, b) {
    return a.level - b.level;
  }).filter(function(leve) {
    return leve.level <= level;
  }).reverse()[0];
}
 
var leveItems = [
  {
    level: 20,
    name: "Goatskin Jacket",
    exp: 19876
  },
  {
    level: 25,
    name: "Goatskin Wristbands",
    exp: 34716
  },
  {
    level: 30,
    name: "Boarskin Satchel Belt",
    exp: 47824
  },
  {
    level: 35,
    name: "Boarskin Ringbands",
    exp: 61552
  },
  {
    level: 40,
    name: "Boarskin Culottes",
    exp: 81322
  },
  {
    level: 45,
    name: "Rapotorskin Artisan's Belt",
    exp: 97716
  },
];

var leveAmounts = {};
var currentExp = calculateExp(21, 17334);
while(currentExp < expTotal[49]) {
  var leve = calculateBestLeve(leveItems, currentExp);
  currentExp += leve.exp * 2;
  leveAmounts[leve.name] = (leveAmounts[leve.name] || 0) + 1;
}

console.log(JSON.stringify(leveAmounts, null, '  '));