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2. Genealogical numbering systems - Wikipedia

   en.wikipedia.org/wiki/Genealogical_numbering_systems

   The number of a person's father is twice their own number, and the number of a person's mother is twice their own, plus one. For instance, if John Smith is 10, his father is 20, and his mother is 21, and his daughter is 5. In order to readily have the generation stated for a certain person, the Ahnentafel numbering may be preceded by the ...

3. Trachtenberg system - Wikipedia

   en.wikipedia.org/wiki/Trachtenberg_system

   Trachtenberg system. The Trachtenberg system is a system of rapid mental calculation. The system consists of a number of readily memorized operations that allow one to perform arithmetic computations very quickly. It was developed by the Russian engineer Jakow Trachtenberg in order to keep his mind occupied while being in a Nazi concentration ...

4. List of country calling codes - Wikipedia

   en.wikipedia.org/wiki/List_of_country_calling_codes

   Zone 1 uses an integrated numbering plan; four digits (1xxx) determine the area served in Canada, the United States and its territories, and much of the Caribbean. Zone 2 uses two 2-digit codes (20, 27) and eight sets of 3-digit codes (21x–26x, 28x, 29x), mostly to serve Africa , but also Aruba , Faroe Islands , Greenland and British Indian ...

5. List of TCP and UDP port numbers - Wikipedia

   en.wikipedia.org/wiki/List_of_TCP_and_UDP_port...

   The port numbers in the range from 0 to 1023 (0 to 2 10 − 1) are the well-known ports or system ports. [3] They are used by system processes that provide widely used types of network services. On Unix-like operating systems, a process must execute with superuser privileges to be able to bind a network socket to an IP address using one of the ...

6. Trace (linear algebra) - Wikipedia

   en.wikipedia.org/wiki/Trace_(linear_algebra)

   Trace (linear algebra) In linear algebra, the trace of a square matrix A, denoted tr (A), [ 1] is defined to be the sum of elements on the main diagonal (from the upper left to the lower right) of A. The trace is only defined for a square matrix ( n × n ). In mathematical physics texts, if tr (A) = 0 then the matrix is said to be traceless.

7. Ultra-high vacuum - Wikipedia

   en.wikipedia.org/wiki/Ultra-high_vacuum

   Ultra-high vacuum (often spelled ultrahigh in American English, UHV) is the vacuum regime characterised by pressures lower than about 1 × 10 −6 pascals (1.0 × 10 −8 mbar; 7.5 × 10 −9 Torr). UHV conditions are created by pumping the gas out of a UHV chamber.

8. Power of 10 - Wikipedia

   en.wikipedia.org/wiki/Power_of_10

   Power of 10. Visualisation of powers of 10 from one to 1 trillion. A power of 10 is any of the integer powers of the number ten; in other words, ten multiplied by itself a certain number of times (when the power is a positive integer). By definition, the number one is a power (the zeroth power) of ten. The first few non-negative powers of ten are:

9. List of prime numbers - Wikipedia

   en.wikipedia.org/wiki/List_of_prime_numbers

   A prime number (or prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. By Euclid's theorem , there are an infinite number of prime numbers. Subsets of the prime numbers may be generated with various formulas for primes .