Viral coefficient

<div class="stage"><div class="label">INVITES / USER <b id="invites">2</b> · JOIN RATE 40%</div><input id="invite-range" type="range" min="1" max="4" value="2"><div class="generations" id="generations"></div><div class="hint">EACH BAR = NEW USERS IN A GENERATION</div></div>

.stage{position:relative;width:min(94vw,760px);height:min(88vh,310px);font:800 clamp(10px,max(3.4vmin,1vw),15px)/1.25 sans-serif}.stage *{box-sizing:border-box}.label{font-size:clamp(10px,max(3.4vmin,1vw),12px);letter-spacing:.1em;color:var(--muted)}.accent{color:var(--accent)}.pill{border:1.5px solid var(--fg);border-radius:999px;background:var(--surface);padding:.5em .8em}.hint{position:absolute;right:2%;bottom:0;font-size:clamp(10px,max(3.4vmin,1vw),12px);color:var(--muted)}.stage input{position:absolute;top:15%;left:3%;width:54%;accent-color:var(--accent)}.generations{position:absolute;inset:35% 3% 12%;display:flex;align-items:end;gap:3%}.generation{flex:1;height:100%;display:flex;flex-direction:column;justify-content:flex-end;text-align:center;font-size:clamp(10px,max(3.4vmin,1vw),14px)}.generation i{display:block;width:100%;height:var(--h);background:var(--accent);margin-bottom:6px;transition:height .4s}.generation:nth-child(even) i{background:var(--fg)}

const range=document.querySelector('#invite-range'),count=document.querySelector('#invites'),bars=document.querySelector('#generations');let auto=0;function draw(){const invitations=Number(range.value),k=invitations*.4;count.textContent=String(invitations);bars.innerHTML=Array.from({length:5},(_,i)=>{const value=Math.pow(k,i),height=Math.max(7,Math.min(100,value*55));return '<div class="generation"><i style="--h:'+height+'%"></i>G'+i+'</div>'}).join('')}range.addEventListener('input',()=>{auto=Date.now();draw()});draw();setInterval(()=>{if(Date.now()-auto<6000)return;range.value=String(Number(range.value)%4+1);draw()},1400);