27. Given $7^{2}=49, 49$ has a sum of digits of $13; 67^{2}=4489, 4489$ has a sum of digits of $25; 667^{2}=444889, 444889$ has a sum of digits of $37, \underbrace{666 \ldots 666}_{15 \uparrow 6} 7^{2}$ has a sum of digits of $\qquad$
Reference answer: 193