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**109** (**one hundred [and] nine**) is the natural number following 108 and preceding 110.

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Cardinal | one hundred nine | |||

Ordinal | 109th (one hundred ninth) | |||

Factorization | prime | |||

Prime | 29th | |||

Divisors | 1, 109 | |||

Greek numeral | ΡΘ´ | |||

Roman numeral | CIX | |||

Binary | 1101101_{2} | |||

Ternary | 11001_{3} | |||

Octal | 155_{8} | |||

Duodecimal | 91_{12} | |||

Hexadecimal | 6D_{16} |

109 is the 29th prime number. As 29 is itself prime, 109 is a super-prime.^{[1]} The previous prime is 107, making them both twin primes.^{[2]} 109 is a centered triangular number.^{[3]}

There are exactly 109 different families of subsets of a three-element set whose union includes all three elements,^{[4]} 109 different loops (invertible but not necessarily associative binary operations with an identity) on six elements, ^{[5]} and 109 squares on an infinite chessboard that can be reached by a knight within three moves.^{[6]}

**109**is the atomic number of meitnerium.^{[7]}- The diameter of the sun is about 109.1 to 109.5 the diameter of the earth.

**^**Sloane, N. J. A. (ed.). "Sequence A006450 (Primes with prime subscripts)".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation.**^**Sloane, N. J. A. (ed.). "Sequence A006512 (Greater of twin primes)".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation.**^**Sloane, N. J. A. (ed.). "Sequence A005448 (Centered triangular numbers)".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation.**^**Sloane, N. J. A. (ed.). "Sequence A003465 (Number of ways to cover an*n*-set)".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation.**^**Sloane, N. J. A. (ed.). "Sequence A057771 (Number of loops (quasigroups with an identity element) of order*n*)".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation.**^**Sloane, N. J. A. (ed.). "Sequence A018836 (Number of squares on infinite chess-board at ≤*n*knight's moves from a fixed square)".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation.**^**Emsley, John (2011),*Nature's Building Blocks: An A-Z Guide to the Elements*, Oxford University Press, p. 316, ISBN 9780199605637.