one of three non-trivial numbers (the other two are
1458 and
1729) which, when its digits (in decimal) are added together, produces a sum which, when multiplied by its reversed self, yields the original number:
8 + 1 = 9
9 × 9 = 81 (although this case is somewhat degenerate, as the sum has only a single digit).
Look up eighty-one in Wiktionary, the free dictionary.
The inverse of 81 is 0.012345679recurring, missing only the digit "8" from the complete set of digits. This is an example of the general rule that, in base b,
one of three non-trivial numbers (the other two are
1458 and
1729) which, when its digits (in decimal) are added together, produces a sum which, when multiplied by its reversed self, yields the original number:
8 + 1 = 9
9 × 9 = 81 (although this case is somewhat degenerate, as the sum has only a single digit).
Look up eighty-one in Wiktionary, the free dictionary.
The inverse of 81 is 0.012345679recurring, missing only the digit "8" from the complete set of digits. This is an example of the general rule that, in base b,