15 (number)
| ||||
---|---|---|---|---|
pentadecimal | ||||
Factorization | 3 × 5 | |||
Divisors | 1, 3, 5, 15 | |||
Greek numeral | ΙΕ´ | |||
Roman numeral | XV | |||
Binary | 11112 | |||
Ternary | 1203 | |||
Senary | 236 | |||
Octal | 178 | |||
Duodecimal | 1312 | |||
Hexadecimal | F16 | |||
Hebrew numeral | ט"ו / י"ה | |||
Babylonian numeral | 𒌋𒐙 |
15 (fifteen) is the natural number following 14 and preceding 16.
Mathematics
15 is:
- The eighth 5, so the first of the form (3.q),[2]where q is a higher prime.
- a binary (1111) and quaternary (33). In hexadecimal, and higher bases, it is represented as F.
- with an 3-aliquot tree.
- the second member of the first cluster of two discrete semiprimes (14, 15); the next such cluster is (21, 22).
- the first number to be polygonal in 3 ways: it is a triangular number, a hexagonal number,[5] and pentadecagonal number.[6]
- a centered tetrahedral number.
- the number of partitions of 7.
- the smallest number that can be factorized using Shor's quantum algorithm.
- the magic constant of the unique order-3 normal magic square.
- the number of supersingular primes.
- the smallest positive number that can be expressed as the difference of two positive squares in more than one way:[7] or (see image).
Furthermore,
- 15's pair.
- The first 15 superabundant numbers are the same as the first 15 colossally abundant numbers.
- In decimal, 15 contains the digits 1 and 5 and is the result of adding together the integers from 1 to 5 (1 + 2 + 3 + 4 + 5 = 15). The only other number with this property (in decimal) is 27.
- There are 15 truncatable primes that are both right-truncatable and left-truncatable:
- There are 15 rooted binary trees with four labeled leaves, both of these being among the types of objects counted by double factorials.
- With only two exceptions, all prime quadruplets enclose a multiple of 15, with 15 itself being enclosed by the quadruplet (11, 13, 17, 19).
- If a positive definite quadratic form with integer matrix represents all positive integers up to 15, then it represents all positive integers via the 15 and 290 theorems.
- 15 is the product of distinct Fermat primes, 3 and 5; hence, a regular pentadecagon is constructiblewith a compass and unmarked straightedge, and is expressible in terms of square roots.
- There are 15 monohedral convex pentagonal tilings, with eight being edge-to-edge.
- There are 15 regular and semiregular tilings when infinite (improper) apeirogonal forms are counted: three are regular (with one self-dual), eight are semiregular (with one chiral), and four are apeirogonal (from a total of 8, in-which 4 are duplicates).
- Full of 5, wherein the sum of the first 5 integers itself is 15. Expressed mathematically:
- , while , and .
- There are 15 Archimedean solids and 15 Catalan solids when enantiomorphic forms are counted separately.
- There are 15 regular honeycombs in hyperbolic 3-space: four are compact, and 11 are paracompact.[8]
- It is the smallest non-trivial Surprise Number. When 15 is partitioned into 2 parts of digits- smaller part 1 and larger part 5, adding numbers from smaller 1 to larger 5 = 1 + 2 + 3 + 4 + 5 = 15 = Original Number.
Science
- The atomic number of phosphorus.
- 15 Eunomia is the largest Eunomian asteroid in the inner asteroid belt.
Religion
Sunnism
The
Hanbali Sunni madhab states that the age of fifteen of a solar or lunar calendar is when one's taklif (obligation or responsibility) begins and is the stage whereby one has his deeds recorded.[9]
Judaism
- In the Hebrew numbering system, the number 15 is not written according to the usual method, with the letters that represent "10" and "5" (י-ה, yodh and heh), because those spell out one of the Jewish names of God. Instead, the date is written with the letters representing "9" and "6" (ט-ו, teth and vav)[citation needed]
References
- ^ Sloane, N. J. A. (ed.). "Sequence A001358 (Semiprimes (or biprimes): products of two primes.)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ^ Sloane, N. J. A. (ed.). "Sequence A001748 (a(n) = 3 * prime(n))". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ^ Sloane, N. J. A. (ed.). "Sequence A000110 (Bell or exponential numbers)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ^ Sloane, N. J. A. (ed.). "Sequence A000332 (Binomial coefficient binomial(n,4) = n*(n-1)*(n-2)*(n-3)/24)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ^ Sloane, N. J. A. (ed.). "Sequence A000384 (Hexagonal numbers)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ^ Sloane, N. J. A. (ed.). "Sequence A051867 (pentadecagonal numbers.)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ^ Sloane, N. J. A. (ed.). "Sequence A334078 (a(n) is the smallest positive integer that can be expressed as the difference of two positive squares in at least n ways.)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- CiteSeerX 10.1.1.361.251.
- ^ Spevack, Aaron (2011). Ghazali on the Principles of Islamic Spiritualit. p. 50.
Further reading
- Wells, D. The Penguin Dictionary of Curious and Interesting Numbers London: Penguin Group. (1987): 91–93
External links
Look up 15 in Wiktionary, the free dictionary.
- Clewett, James. "15: f in hexadecimal". Numberphile. Brady Haran. Archived from the original on 2013-05-16. Retrieved 2013-04-02. – discussing hexadecimals
- Bowley, Roger. "15: Bumfit". Numberphile. Brady Haran. Archived from the original on 2013-05-16. Retrieved 2013-04-01. – discussing the Celtic number as used in Lincolnshire