The article is written in Japanese, but I thought the idea would be obvious enough from the picture (and the linked source code) even if you don't read Japanese. In case you are wondering, here is a translation.

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11111111111122211111111111122622111111999992266211119999999222221119999999966666111999999999996611166622622266661162262262222266116226622222222611622662226222261662222266666661166662222666626111166222222226611111999966966661166666699696661166666666966966116666666699696111662266669966911162222669999621112222269992999111222229999999911121229999999991161229999999999166111999999999666611169999999966666669669999996666666999669999666666699999119966666669999911111111666999911111111166111111111111116111111111111111

is a 512-digit prime number. When fit in a 16 x 32 rectangle, it will be:

    1111111111112221
    1111111111122622
    1111119999922662
    1111999999922222
    1119999999966666
    1119999999999966
    1116662262226666
    1162262262222266
    1162266222222226
    1162266222622226
    1662222266666661
    1666622226666261
    1116622222222661
    1111999966966661
    1666666996966611
    6666666696696611
    6666666699696111
    6622666699669111
    6222266999962111
    2222269992999111
    2222299999999111
    2122999999999116
    1229999999999166
    1119999999996666
    1116999999996666
    6669669999996666
    6669996699996666
    6669999911996666
    6669999911111111
    6669999111111111
    6611111111111111
    6111111111111111
    

which can be colored: (Super Mario appears)