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  2. Extended periodic table - Wikipedia

    en.wikipedia.org/wiki/Extended_periodic_table

    The configurations of the elements in this table are written starting with [Og] because oganesson is expected to be the last prior element with a closed-shell (inert gas) configuration, 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 5f 14 6s 2 6p 6 6d 10 7s 2 7p 6. Similarly, the [172] in the configurations for elements ...

  3. Negative number - Wikipedia

    en.wikipedia.org/wiki/Negative_number

    This thermometer is indicating a negative Fahrenheit temperature (−4 °F). In mathematics, a negative number is the opposite of a positive real number. [1] Equivalently, a negative number is a real number that is less than zero. Negative numbers are often used to represent the magnitude of a loss or deficiency.

  4. Plus and minus signs - Wikipedia

    en.wikipedia.org/wiki/Plus_and_minus_signs

    In chemistry, superscripted plus and minus signs are used to indicate an ion with a positive or negative charge of 1 (e.g., NH + 4 ). If the charge is greater than 1, a number indicating the charge is written before the sign (as in SO 2− 4 ).

  5. Subtraction - Wikipedia

    en.wikipedia.org/wiki/Subtraction

    = (pronounced as "four minus six equals negative two") There are also situations where subtraction is "understood", even though no symbol appears: [ citation needed ] A column of two numbers, with the lower number in red, usually indicates that the lower number in the column is to be subtracted, with the difference written below, under a line.

  6. Countable set - Wikipedia

    en.wikipedia.org/wiki/Countable_set

    In mathematics, a set is countable if either it is finite or it can be made in one to one correspondence with the set of natural numbers. [a] Equivalently, a set is countable if there exists an injective function from it into the natural numbers; this means that each element in the set may be associated to a unique natural number, or that the elements of the set can be counted one at a time ...

  7. List of sums of reciprocals - Wikipedia

    en.wikipedia.org/wiki/List_of_sums_of_reciprocals

    Then the triangle is in Euclidean space if the sum of the reciprocals of p, q, and r equals 1, spherical space if that sum is greater than 1, and hyperbolic space if the sum is less than 1. A harmonic divisor number is a positive integer whose divisors have a harmonic mean that is an integer. The first five of these are 1, 6, 28, 140, and 270 ...

  8. Additive inverse - Wikipedia

    en.wikipedia.org/wiki/Additive_inverse

    In modular arithmetic, the modular additive inverse of x is the number a such that a + x ≡ 0 (mod n) and always exists. For example, the inverse of 3 modulo 11 is 8, as 3 + 8 ≡ 0 (mod 11). [12] In a Boolean ring, which has elements {,} addition is often defined as the symmetric difference.

  9. Parity (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Parity_(mathematics)

    The division of two whole numbers does not necessarily result in a whole number. For example, 1 divided by 4 equals 1/4, which is neither even nor odd, since the concepts of even and odd apply only to integers. But when the quotient is an integer, it will be even if and only if the dividend has more factors of two than the divisor. [6]