Since the flag starts with `texsaw`, we can deduce that the first 6 numbers correspond with [116, 101, 120, 115, 97, 119].

With 6 data points we can set up a polynomial of degree 5 to fit the first 6 numbers. `ax^5 + bx^4 + cx^3 + dx^2 + ex + f = res`.

116^5a + 116^4b + 116^3c + 116^2d + 116e + f = 1014193795365553418
101^5a + 101^4b + 101^3c + 101^2d + 101e + f = 507858563019110228
120^5a + 120^4b + 120^3c + 120^2d + 120e + f = 1201348919167710110
115^5a + 115^4b + 115^3c + 115^2d + 115e + f = 971265549232012470
97^5a + 97^4b + 97^3c + 97^2d + 97e + f = 415042311506972496
119^5a + 119^4b + 119^3c + 119^2d + 119e + f = 1152164036977568522

We then can use quickmath to compute system of equations to solve for the six variables.

We found that a = 48066976, b = 24705178, c = 95573334, d = 50141857, e = 28353433, f = 88125350

Finally, we can write a python code to recover the rest of Xs values

for each element x in ciphertext array:
for i from 0 to 255:
res -> ax^5 + bx^4 + cx^3 + dx^2 + ex + f
if res = x
add to flag

The flag comes out to be `texsaw{Ju5t_Som3_B45ic_M4th}`