User blog comment:Deedlit11/Bignum Bakeoff appetizer/@comment-2033667-20140918095057/@comment-5529393-20140918095551

What about

k = 9 << 99999, b = 1;

u(n,i,o) { while (i++, n / o) o *= b; return n ? pow(b + 1, u(i)) + u(n - o / b) : n; }

main { while (b++, k = u(--k,-1,1)); return b; }

gets 118 characters.