Untouchable Number
A untouchable number is a Entier naturalness which cannot be expressed like the nap of the clean dividing of an entirety. The first untouchable small numbers are:
2, 5, 52, 88, 96, 120, 124, 146, 162, 188, 206, 210, 216, 238, 246, 248, 262, 268, 276, 288, 290, 292, 304, 306, 322, 324, 326, 336, 342, 372, 406, 408, 426, 430, 448, 472, 474, 498, 516, 518, 520, 530, 540, 552, 556, 562, 576, 584, 612, 624, 626, 628, 658
electronic Encyclopedia of the whole continuations (id=A005114)
5 is recognized like the only untouchable number odd, but this was not shown. No Perfect number is untouchable, since they can be expressed as the sum of their clean Diviseur S.
Paul Erdős proved that there exists an infinity of untouchable numbers.
Example of nonuntouchable number
To prove that a number is not untouchable makes it possible to better include/understand the definition.
For example, 9 is not untouchable, because 15 have as clean dividers 5,3,1, and 9 = 1+3+5.
See too
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