Tall-leksikon - Matematikk på nett - Nordreisa videregående skole

Dagens tall:
• Primtall, faktorene 1 og 7
7
(From Wikipedia, the free encyclopedia)
• Ulike former: VII – romertall, ፯ - amarisk, ٧ – arabisk, ৭ – bengalsk, 七,柒 – kinesisk, ७ –
devanagarisk, ז – hebraisk, ៧ - khmar, ๗ – thai
• Forstavelse hepta- eller hept- fra gresk og sept- fra latin
• Binært 111, tretallssystem 21, firetalls 13, femtalls 12, sekstalls 11, sjutalls 10, oktalt 7, tolvtallssystem
7, heksadesimalt 7
• Et natulig tall som leigger mellom 6 og 8. Det minste positive heltallet som uttales med to stavelser på
engelsk.
Resten er engelsk – tatt direkte fra Wikipedia:
• Seven is the fourth prime number. It is not only a Mersenne prime (since 2 3 − 1 = 7) but also a double
Mersenne prime since it is itself the exponent for another Mersenne prime (127). It is also a Newman-
Shanks-Williams prime, a Woodall prime, a factorial prime, a lucky prime, a happy number, a safe
prime and the fourth Heegner number.
• Seven is the only number less than 15 which cannot be represented as the sum of the squares of three
integers.
• Seven is the aliquot sum of one number, the cubic number 8 and is the base of the 7-aliquot tree. It is
also said to be a lucky number
• n = 7 is the first natural number for which the next statement does not hold: "Two nilpotent
endomorphisms from C n with the same minimal polynomial and the same rank are similar."
• 7 is the only dimension, besides the familiar 3, in which a vector cross product can be defined [citation
needed] .
• 999,999 divided by 7 is exactly 142,857. Therefore, when a vulgar fraction with 7 in the denominator
is converted to a decimal expansion, the result has the same six-digit repeating sequence after the
decimal point, but the sequence can start with any of those six digits. [1] For example,
1/7 = 0.142 857 142.... and 2/7 = 0.285 714 285...
• A seven-sided shape is a heptagon. The regular n-gons for n ≤ 6 can be constructed by compass and
straightedge alone, but the regular heptagon cannot. Figurate numbers representing heptagons
(including seven) are called heptagonal numbers. Seven is also a centered hexagonal number.
• There are seven frieze groups, the groups consisting of symmetries of the plane whose group of
translations is isomorphic to the group of integers.
• There are seven fundamental types of catastrophes.
• Seven is the sum of any two opposite sides on a standard six-sided die. When rolling two standard sixsided
dice, seven has a 6 in 36 (or 1/6th) probability of being rolled (1–6, 6–1, 2–5, 5–2, 3–4, or 4–3),
the greatest of any number.
• The Millennium Prize Problems are seven problems in mathematics that were stated by the Clay
Mathematics Institute in 2000. Currently, six of the problems remain unsolved.
• In the beginning, various Hindus wrote 7 more or less in one
stroke as a curve that looks like an uppercase J vertically
inverted. The western Ghubar Arabs' main contribution was
to make the longer line diagonal rather than straight, though
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