Can create stubs that look random to the average Joe.

encodeStub-decodeStub.js

var encodeStub, decodeStub;
(function() {
  function encodeNumber(number, minNumber, maxNumber, maxPerSeries) {
    var offset = minNumber;
    var limitNumber = maxNumber - offset + 1;
  
    var maxMaxPerSeries = Math.ceil(limitNumber / 2);
    maxPerSeries = Math.floor(maxPerSeries);
    if (!(1 <= maxPerSeries && maxPerSeries <= maxMaxPerSeries)) {
      throw new Error('Since there are ' + limitNumber + ' possible values the maxPerSeries must be between 1 and ' + maxMaxPerSeries + '.');
    }
    
    var step = Math.ceil(limitNumber / maxPerSeries);
  
    number = ((number - offset) % limitNumber + limitNumber) % limitNumber;
  
    var series = Math.floor(number / maxPerSeries);
    var positionInSeries = number % maxPerSeries;
  
    return series + positionInSeries * step + offset;
  }
  
  function encode(number, maxPerSeries, alphabet, length) {
    var alphabetLength = alphabet.length;
    var minNumber = 0;
    var maxNumber = Math.pow(alphabet.length, length) - 1;
    if (maxNumber > Number.MAX_SAFE_INTEGER) {
      var maxLength = Math.log(Number.MAX_SAFE_INTEGER) / Math.log(alphabetLength);
      throw new Error('The maximum code length is ' + maxLength + ' for the given alphabet.');
    }
  
    number = encodeNumber(number, minNumber, maxNumber, maxPerSeries) - minNumber;
    for (var code = '', i = 0; i < length; i++) {
      var charIndex = number % alphabetLength;
      number = Math.floor(number / alphabetLength);
      code += alphabet.charAt(charIndex);
    }
    return code;
  }
  

  function decodeNumber(number, minNumber, maxNumber, maxPerSeries) {
    var offset = minNumber;
    var limitNumber = maxNumber - offset + 1;
  
    var maxMaxPerSeries = Math.ceil(limitNumber / 2);
    maxPerSeries = Math.floor(maxPerSeries);
    if (!(1 <= maxPerSeries && maxPerSeries <= maxMaxPerSeries)) {
      throw new Error('Since there are ' + limitNumber + ' possible values the maxPerSeries must be between 1 and ' + maxMaxPerSeries + '.');
    }
    
    var step = Math.ceil(limitNumber / maxPerSeries); // 3
  
    number = ((number - offset) % limitNumber + limitNumber) % limitNumber; // 5
  
    var series = Math.floor(number / step); // 1
    var positionInSeries = number % step; // 2
  
    return series + positionInSeries * maxPerSeries + offset;
  }
  
  function decode(code, maxPerSeries, alphabet) {
    var alphabetLength = alphabet.length;
    var length = code.length;
   
    var minNumber = 0;
    var maxNumber = Math.pow(alphabet.length, length) - 1;
    if (maxNumber > Number.MAX_SAFE_INTEGER) {
      throw new Error('This code cannot be decoded reliably due to JavaScript integer limitation.');
    }
  
    for (var number = 0, i = length; i--; ) {
      var char = code.charAt(i);
      number = number * alphabetLength + alphabet.indexOf(char);
    }
    return decodeNumber(number, minNumber, maxNumber, maxPerSeries);
  }
  

  // Some lower case letters and digits 2-9.
  // Omit some characters to avoid confusion when writing down by hand.
  // var STUB_ALPHABET = 'abcdefghijkmnopqrstuvwxyz23456789';
  var STUB_ALPHABET = 'h6y2fusga8ben3dpwij95qm7vktoxcz4r';
  var STUB_CODE_LENGTH = 6;
  var STUB_MAX_PER_SERIES = 29;
  
  encodeStub = function(id) {
    return encode(id - 1, STUB_MAX_PER_SERIES, STUB_ALPHABET, STUB_CODE_LENGTH).replace(/^(...)(...)$/, '$1-$2');
  }
  
  decodeStub = function(stub) {
    return decode(stub.replace(/-/g, ''), STUB_MAX_PER_SERIES, STUB_ALPHABET) + 1;
  }
})();

~example.js

// HIDE \\
console.load('local://encodeStub-decodeStub.js');

//\\
for (var id = 1; id <= 25; id++) {
  var stub = encodeStub(id);
  var decodedId = decodeStub(stub);
  console.log(`${id} \u21E8 ${stub} \u21E8 ${decodedId}`);
}

https://www.yourjs.com/console/?gist=229ab706ddf29c4694ddc03b23c8ba16&file=~example.js&skipIntro=1