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

(C) Some more optimizations to the 125-character winner down to 121. Untested as of yet.

k = 9 << 99999, b = 1;

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

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