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Weird number. In number theory, a weird number is a natural number that is abundant but not semiperfect. [1] [2] In other words, the sum of the proper divisors ( divisors including 1 but not itself) of the number is greater than the number, but no subset of those divisors sums to the number itself.
An abundant number which is not a semiperfect number is called a weird number. An abundant number with abundance 1 is called a quasiperfect number , although none have yet been found. Every abundant number is a multiple of either a perfect number or a primitive abundant number.
Glossary of mathematical symbols. A mathematical symbol is a figure or a combination of figures that is used to represent a mathematical object, an action on mathematical objects, a relation between mathematical objects, or for structuring the other symbols that occur in a formula. As formulas are entirely constituted with symbols of various ...
List of unusual units of measurement. An unusual unit of measurement is a unit of measurement that does not form part of a coherent system of measurement, especially because its exact quantity may not be well known or because it may be an inconvenient multiple or fraction of a base unit.
The number of 10-happy numbers up to 10 n for 1 ≤ n ≤ 20 is [9] 3, 20, 143, 1442, 14377, 143071, 1418854, 14255667, 145674808, 1492609148, 15091199357, 149121303586, 1443278000870, 13770853279685, 130660965862333, 1245219117260664, 12024696404768025, 118226055080025491, 1183229962059381238, 12005034444292997294.
A possible computing problem in the 1990's that was supposed to have occurred when the 21st century and 3rd millennium arrived. Of course, that never happened. Year 2038 problem. The computing problem that will arise due to the Unix time representation used in many computers. Year zero.
An imaginary number is the product of a real number and the imaginary unit i, which is defined by its property i 2 = −1. [1] [2] The square of an imaginary number bi is − b 2 . For example, 5 i is an imaginary number, and its square is −25 .
The two's complement of an integer is computed by: Step 1: starting with the absolute binary representation of the number, with the leading bit being a sign bit; [3] Step 2: inverting (or flipping) all bits – changing every 0 to 1, and every 1 to 0; Step 3: adding 1 to the entire inverted number, ignoring any overflow.
A mathematical coincidence is said to occur when two expressions with no direct relationship show a near-equality which has no apparent theoretical explanation. For example, there is a near-equality close to the round number 1000 between powers of 2 and powers of 10:
The first few unusual numbers are. 2, 3, 5, 6, 7, 10, 11, 13, 14, 15, 17, 19, 20, 21, 22, 23, 26, 28, 29, 31, 33, 34, 35, 37, 38, 39, 41, 42, 43, 44, 46, 47, 51, 52, 53, 55, 57, 58, 59, 61, 62, 65, 66, 67, ... (sequence A064052 in the OEIS) The first few non-prime (composite) unusual numbers are.