Any number greater than 4.
'The electronic I Ching calculator was badly made. It had probably been manufactured in whichever of the South-East Asian countries was busy tooling up to do to South Korea what South Korea was busy doing to Japan. Glue technology had obviously not progressed in that country to the point where things could be successfully held together with it. Already the back had half fallen off and needed to be stuck back on with Sellotape.'
'It was much like an ordinary pocket calculator, except that the LCD screen was a little larger than usual, in order to accommodate the abridged judgments of King Wen on each of the sixty-four hexagrams, and also the commentaries of his son, the Duke of Chou, on each of the lines of the hexagram. These were unusual texts to see marching across the display of a pocket calculator, particularly as they had been translated from the Chinese via the Japanese and seemed to have enjoyed many adventures on the way.'
'The device also functioned as an ordinary calculator, but only to a limited degree. It could handle any calculation which returned an answer of anything up to "4".'
'"1 + 1" it could manage ("2"), and "1 + 2" ("3") and "2 + 2" ("4") or "tan 74" ("3.4874145"), but anything above "4" it represented merely as "A Suffusion of Yellow". Dirk was not certain if this was a programming error or an insight beyond his ability to fathom, but he was crazy about it anyway, enough to hand over £20 of ready cash for the thing.'
--Douglas Adams, "The Long Dark Tea-Time of the Soul"