We want to find M=180⁵⁹ mod 391.

1802 =32400=82×391+ 338 ≡ 338 mod 391.

1803 =5832000=14915×391+ 235 ≡ 235 mod 391.

18059 =(180)2(1803)19 ≡ 338 ×23519 ≡ (2352)9 ×235 ×338 ≡ (55225)9 ×79430 ≡ (141×391+94)9 ×(203×391+57) ≡ 949 ×57 ≡ 8305843 ×57 ≡ (2124×391+100)3×57 ≡ 57000000 ≡ 20 mod 391