# a+certain+number+of

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**Effective atomic number**— has two different meanings: one that is the effective nuclear charge of an atom, and one that calculates the average atomic number for a compound or mixture of materials. Both are abbreviated Zeff.For an atomThe effective atomic number Zeff,… …122

**Friendly number**— In number theory, a friendly number is a natural number that shares a certain characteristic called abundancy, the ratio between the sum of divisors of the number and the number itself, with one or more other numbers. Two numbers with the same… …123

**Directive on rental right and lending right and on certain rights related to copyright in the field of intellectual property**— EU directive title=Directive on rental right and lending right and on certain rights related to copyright in the field of intellectual property number=92/100/EEC madeby=European Council madeunder=Arts. 57(2), 66 100a OJref=L346, 1992 11 27, p. 61 …124

**Bank card number**— A bank card number is the primary account number found on credit cards and bank cards. It has a certain amount of internal structure and shares a common numbering scheme. Credit card numbers are a special case of ISO/IEC 7812 bank card numbers.… …125

**Rational number**— In mathematics, a rational number is any number that can be expressed as the quotient or fraction a/b of two integers, with the denominator b not equal to zero. Since b may be equal to 1, every integer is a rational number. The set of all… …126

**Cryptographically secure pseudorandom number generator**— A cryptographically secure pseudo random number generator (CSPRNG) is a pseudo random number generator (PRNG) with properties that make it suitable for use in cryptography. Many aspects of cryptography require random numbers, for example: Key… …127

**86 (number)**— 86 (eighty six) is the natural number following 85 and preceding 87. ← 85 87 → 86 ← 80 …128

**74 (number)**— 74 (seventy four) is the natural number following 73 and preceding 75. A seventy four was a third rate warship with 74 guns. ← 73 75 → 74 …