# Double-Struck Capital R ℝ

## Symbol Meaning

The set of real numbers ℝ can be best understood as all the finite and infinite decimal fractions. ℝ is the first known uncountable set. The term “real” comes from the Latin word “realis,” meaning “actual” or “real.”

By the 3rd century, it became clear that rational numbers were not sufficient for representing distances in geometry. A comprehensive theory of real numbers emerged in the 19th century with the development of mathematical analysis.

The sets ℕ, ℤ, ℚ, ℝ, ℂ are often written in bold font (for example, in the works of Nicolas Bourbaki) or as double-struck letters on blackboards and manuscripts. American mathematicians introduced the usage of double-struck font in printed texts, and it became popularized with the famous textbook on complex analysis by Gunning and Rossi, published in 1965.

The symbol “Double-Struck Capital R” is included in the “Letterlike symbols” subblock of the “Letterlike Symbols” block and was approved as part of Unicode version 1.1 in 1993.

Text is also available in the following languages: Español; Русский;

### Synonyms

the set of real numbers.

Unicode Name | Double-Struck Capital R |

Unicode Number | |

HTML Code | |

CSS Code | |

Entity | ℝ |

Plane | 0: Basic Multilingual Plane |

Unicode Block | Letterlike Symbols |

Unicode Subblock | Letterlike symbols |

Unicode Version | 1.1 (1993) |

Type of paired mirror bracket (bidi) | None |

Composition Exclusion | No |

Case change | 211D |

Simple case change | 211D |

Math | + |

Alphabetic | + |

Uppercase | + |

Cased | + |

ID_Start | + |

ID_Continue | + |

XID_Start | + |

XID_Continue | + |

Grapheme_Base | + |

scripts | Common |

Other_Math | + |

Encoding | hex | dec (bytes) | dec | binary |
---|---|---|---|---|

UTF-8 | E2 84 9D | 226 132 157 | 14845085 | 11100010 10000100 10011101 |

UTF-16BE | 21 1D | 33 29 | 8477 | 00100001 00011101 |

UTF-16LE | 1D 21 | 29 33 | 7457 | 00011101 00100001 |

UTF-32BE | 00 00 21 1D | 0 0 33 29 | 8477 | 00000000 00000000 00100001 00011101 |

UTF-32LE | 1D 21 00 00 | 29 33 0 0 | 488701952 | 00011101 00100001 00000000 00000000 |