# 229 (number)

| ||||
---|---|---|---|---|

Cardinal | two hundred twenty-nine | |||

Ordinal |
229th (two hundred and twenty-ninth) | |||

Factorization | 229 | |||

Prime | yes | |||

Roman numeral | CCXXIX | |||

Binary |
11100101_{2} | |||

Ternary |
22111_{3} | |||

Quaternary |
3211_{4} | |||

Quinary |
1404_{5} | |||

Senary |
1021_{6} | |||

Octal |
345_{8} | |||

Duodecimal |
171_{12} | |||

Hexadecimal |
E5_{16} | |||

Vigesimal |
B9_{20} | |||

Base 36 |
6D_{36} |

**229** (**two hundred [and] twenty-nine**) is the natural number following 228 and preceding 230.

It is a prime number, and a regular prime.^{[1]}
It is also a full reptend prime, meaning that the decimal expansion of the unit fraction 1/229 repeats periodically with as long a period as possible.^{[2]}
With 227 it is the larger of a pair of twin primes,^{[3]}
and it is also the start of a sequence of three consecutive squarefree numbers.^{[4]} It is the smallest prime that, when added to the reverse of its decimal representation, yields another prime: 229 + 922 = 1151.^{[5]}

There are 229 cyclic permutations of the numbers from 1 to 7 in which none of the numbers is mapped to its successor (mod 7),^{[6]}
229 rooted tree structures formed from nine carbon atoms,^{[7]}
and 229 triangulations of a polygon formed by adding three vertices to each side of a triangle.^{[8]}
There are also 229 different projective configurations of type (12_{3}12_{3}), in which twelve points and twelve lines meet with three lines through each of the points and three points on each of the lines,^{[9]} all of which may be realized by straight lines in the Euclidean plane.^{[10]}^{[11]}

The complete graph *K*_{13} has 229 crossings in its straight-line drawing with the fewest possible crossings.^{[12]}^{[13]}

## References

- ↑ "Sloane's A007703 : Regular primes".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ "Sloane's A001913 : Full reptend primes: primes with primitive root 10".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ "Sloane's A006512 : Greater of twin primes".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ "Sloane's A007675 : Numbers n such that n, n+1 and n+2 are squarefree".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ "Sloane's A061783 : Primes p such that p + (p reversed) is also a prime".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ "Sloane's A000757 : Number of cyclic permutations of [n] with no i->i+1 (mod n)".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ "Sloane's A000678 : Number of carbon (rooted) trees with n carbon atoms = unordered 4-tuples of ternary trees".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ "Sloane's A087809 : Number of triangulations (by Euclidean triangles) having 3+3n vertices of a triangle with each side subdivided by n additional points".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ "Sloane's A001403 : Number of combinatorial configurations of type (n_3)".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ "Sloane's A099999 : Number of geometrical configurations of type (n_3)".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ Gropp, Harald (1997), "Configurations and their realization",
*Discrete Mathematics*,**174**(1–3): 137–151, doi:10.1016/S0012-365X(96)00327-5. - ↑ "Sloane's A014540 : Rectilinear crossing number of complete graph on n nodes".
*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. - ↑ Aichholzer, Oswin; Krasser, Hannes (2007), "Abstract order type extension and new results on the rectilinear crossing number",
*Computational Geometry*,**36**(1): 2–15, doi:10.1016/j.comgeo.2005.07.005, MR 2264046.

## See also

- Area code 229, assigned to Albany, Georgia, USA
- List of highways numbered 229