43
43 is a prime number, the atomic number of technetium — the first element ever produced artificially — and forms a twin-prime pair with 41.
- Odd
- Prime
Where 43 fits
Why 43 is special
43's element, technetium, is scientifically notable in its own right: every atom of it in a lab was made by humans, none found naturally on Earth in any practical quantity.
Same number, different meanings
How 43 is understood across different contexts — never implying one meaning because of another.
- Mathematics
43's element, technetium, is scientifically notable in its own right: every atom of it in a lab was made by humans, none found naturally on Earth in any practical quantity.
- Everyday life
Element 43 has no stable isotope, yet one of its unstable forms is used more than any other radioisotope in medicine. Technetium-99m emits a gamma ray convenient for imaging and has a half-life of about six hours — long enough for a scan, short enough to clear the patient quickly — and it is used in the large majority of nuclear-medicine procedures. Because it decays so fast it cannot be stockpiled, so hospitals extract it on site from generators, and reactor shutdowns in 2009-2010 caused a worldwide shortage of scans.
- Geography
+43 reaches Austria, in the 4x block the ITU allocated to central and western Europe alongside +41 Switzerland, +44 the United Kingdom and +49 Germany. Austrian numbers vary in length by region, so the total digit count is not a reliable check on whether one has been written correctly.
- Science
43 is the atomic number of technetium, the first chemical element to be produced artificially rather than found in nature.
43 is part of
Factors & digit properties
- Divisors (2)
- 1, 43
- Prime factorisation
- 43
- Digit sum
- 7
- Digital root
- 7
Representations
- Decimal
- 43
- Scientific notation
- 4.300 × 10^1
Roman numerals
X L I I I
XLIII uses the subtractive pair XL: ten before fifty — fifty minus ten.
Binary
1 0 1 0 1 1
1 × 32 + 0 × 16 + 1 × 8 + 0 × 4 + 1 × 2 + 1 × 1 = 43
Octal
5 3
5 × 8 + 3 × 1 = 43
Hexadecimal
2 b
2 × 16 + b × 1 = 43
Read as powers of two: 32 + 8 + 2 + 1 = 43.
In historical numeral systems
Egyptian
4 hobbles, 3 strokes
4 × 10 + 3 × 1 = 43. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
4 corner wedges + 3 vertical wedges
43 fits in a single sexagesimal place: 4 corner wedges + 3 vertical wedges.
Greek (Ionic)
mu, then gamma, marked as a numeral
mu-gamma + keraia
mu + gamma written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
mem, then gimel
mem-gimel
mem (40) + gimel (3) = 43, written in descending order.
Chinese numerals
sì shí sān
sì shí sān
四 before 十 multiplies it: 4 tens. 三 after it adds 3. The written form mirrors the arithmetic — "sì shí sān". The financial (anti-fraud) form is 肆拾參.
Maya
2 dots (upper, twenties place) over 3 dots (lower, units place)
2 × 20 + 3 = 43. Places stack vertically with the smallest at the bottom, so the upper group is worth twenty times the lower.
Systems that simply cannot reach this value are left out. Where a script needs a font most readers do not have, the reading is given instead of the glyphs — see number systems for each system in full.
Other mathematical patterns
- Deficient number
- Lucky number (mathematical sieve)
- Twin prime
Related numbers & connections
43 is a factor of 86 (43 × 2 = 86).
View 86 →41 and 43 are twin primes — two primes exactly two apart.
View 41 →Everyday life
Element 43 has no stable isotope, yet one of its unstable forms is used more than any other radioisotope in medicine. Technetium-99m emits a gamma ray convenient for imaging and has a half-life of about six hours — long enough for a scan, short enough to clear the patient quickly — and it is used in the large majority of nuclear-medicine procedures. Because it decays so fast it cannot be stockpiled, so hospitals extract it on site from generators, and reactor shutdowns in 2009-2010 caused a worldwide shortage of scans.
DocumentedEveryday lifePeriod: 1960s – present
Geography
+43 reaches Austria, in the 4x block the ITU allocated to central and western Europe alongside +41 Switzerland, +44 the United Kingdom and +49 Germany. Austrian numbers vary in length by region, so the total digit count is not a reliable check on whether one has been written correctly.
DocumentedGeographyGeography: Austria
Science
43 is the atomic number of technetium, the first chemical element to be produced artificially rather than found in nature.
DocumentedScience
Mathematics
43 is prime, and forms a twin-prime pair with 41.
DocumentedMathematics
Common questions
Why is element 43 not found in nature?
Technetium has no stable isotope, and its longest-lived forms decay far faster than the Earth is old, so any that existed when the planet formed is long gone. Traces occur in uranium ores as a fleeting decay product. Every practical quantity is made deliberately — and one of its isotopes, technetium-99m, is used in most nuclear-medicine scans.
Is 43 a prime number?
Yes, 43 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 43?
The factors of 43 are 1, 43.
What is 43 in Roman numerals?
43 in Roman numerals is XLIII. XL is subtractive: ten before fifty — fifty minus ten. Written additively it would be XXXXIII, which Roman inscriptions used freely — the strict subtractive form is a later convention.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 4 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026