Numberwise

1668

1668 is the year Newton built the first practical reflecting telescope.

3 confirmed records · 2 sourcesChecked and sourcedChecked, general knowledgeHow we qualify claimsReport a correction

Where 1668 fits

Where 1668 fits: History, Related numbersHistory: Historical years. Related numbers: 1640, 1672, 1656, 1435.HistoryHistorical yearsRelated numbers16401672165614351668
1668 connects to 2 worlds: history, related numbers.

Why 1668 is special

Mirrors avoid the colour fringing that lenses produce. Almost every large telescope since, including Hubble and Webb, is a reflector.

1668 is part of

Numbers around us

Factors & digit properties

Divisors (12)
1, 2, 3, 4, 6, 12, 139, 278, 417, 556, 834, 1668
Prime factorisation
2^2 × 3 × 139
Digit sum
21
Digital root
3

Representations

Decimal
1668
Scientific notation
1.668 × 10^3

Roman numerals

M D C L X V I I I

Binary

1 1 0 1 0 0 0 0 1 0 0

1 × 1,024 + 1 × 512 + 0 × 256 + 1 × 128 + 0 × 64 + 0 × 32 + 0 × 16 + 0 × 8 + 1 × 4 + 0 × 2 + 0 × 1 = 1,668

Octal

3 2 0 4

3 × 512 + 2 × 64 + 0 × 8 + 4 × 1 = 1,668

Hexadecimal

6 8 4

6 × 256 + 8 × 16 + 4 × 1 = 1,668

Read as powers of two: 1,024 + 512 + 128 + 4 = 1,668.

In historical numeral systems

Egyptian

1 lotus, 6 coils of rope, 6 hobbles, 8 strokes

1 × 1,000 + 6 × 100 + 6 × 10 + 8 × 1 = 1,668. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.

Babylonian

2 corner wedges + 7 vertical wedges (sixties place), 4 corner wedges + 8 vertical wedges (units place)

27 × 60 + 48 = 1668. Places are separated by a space on the tablet, with the higher place written first.

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

  • Abundant number

Related numbers & connections

Documented appearance
1668 is a year in the 17th century, in the 1660s.

1668 is a year in the 17th century, in the 1660s.

Connection
Portugal declared independence from Spain in 1640 and Spain recognised it in 1668 — a coup that took a day and a war that took twenty-eight years.

Portugal declared independence from Spain in 1640 and Spain recognised it in 1668 — a coup that took a day and a war that took twenty-eight years.

View 1640 →

Numbers Around Us

  • appears inHistorical years
    why?

    Strength 0.50, confidence "high".

Other connections

  • developed from1640
    why?

    Strength 0.50, confidence "high".

  • is associated with1672
    why?

    Strength 0.50, confidence "high".

  • developed from1656
    why?

    Strength 0.50, confidence "high".

  • contrasts with1435
    why?

    Strength 0.50, confidence "high".

How is 1668 connected to another number? →

Technology & computing

  • In 1668, Isaac Newton built the first working reflecting telescope (England).

    DocumentedTechnology & computingGeography: EnglandPeriod: 1668

  • Newton's 1668 reflector used a mirror rather than a lens, avoiding chromatic aberration and the impractical lengths refractors required. Every major telescope built since follows that choice.

    DocumentedTechnology & computingGeography: EnglandPeriod: 1668

  • Spain built its conventional railways to Iberian gauge and its high-speed lines to standard gauge, so it operates both. Some trains have variable-gauge axles that change while moving slowly through a trackside device.

    DocumentedTechnology & computingGeography: Spain and Portugal

Common questions

Is 1668 a prime number?

No, 1668 is not prime.

What are the factors of 1668?

The factors of 1668 are 1, 2, 3, 4, 6, 12, 139, 278, 417, 556, 834, 1668.

What is 1668 in Roman numerals?

1668 in Roman numerals is MDCLXVIII.

About this page's data

Mathematical facts:computed directly from the number's value — nothing to source or verify externally.

Contextual records: 3 reviewer-confirmed records, sourced and reviewed before publication.

Last reviewed: 15 July 2026