JavaScript (ES6), 28 bytes
n=>g=(x=2)=>++n%x?--x:g(++x)
Test it
o.innerText=(f=
n=>g=(x=2)=>++n%x?--x:g(++x)
)(i.value=2521)();oninput=_=>o.innerText=f(+i.value)()<input id=i><pre id=o>
Shaggy
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