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Javascript, 388-50=338

l="length";function g(n){for(;m(++n););p.push(n)}function m(n){for(i=0;i<p[l];i++)if(n%p[i]==0)return 1;return 0}function f(n,x,q,o){while(p[p[l]-1]<n)g(2);if(p.indexOf(n)>=0||n==1)return n;q=[];while(q[l]<=n)q.push(0);for(i=0;i<p[l];i++){x=p[i];while(n%x==0){q[x]++;n/=x}}o="";for(i=2;i<q[l];i++)if(q[i]){if(o)o+="*";o+=i;if(q[i]>1){o+="^{"+f(q[i])+"}"}}return o}alert(f(+prompt(p=[2])))

Since LATEX code is now eligible for the bonus, I decided to include the requisite modifications as part of the golfing for this. It can probably still be golfed further though.