Number

91

91 is a composite number, odd, a calendar year.

Arithmetic Number Deficient Number Flippable Happy Number Hexagonal Odious Number Pernicious Number Recamán's Sequence Semiprime Square Pyramidal Squarefree Triangular Year

Historical context — 91 AD

Calendar year

AD 91 (XCI) was a common year starting on Saturday of the Julian calendar.

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Historical context — 91 BC

Calendar year

Year 91 BC was a year of the pre-Julian Roman calendar.

Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 · English fallback Read the full article on Wikipedia →

Year facts

Year type: Common year
Standard 365-day year; not divisible by 4 (or divisible by 100 but not 400).
Days in year: 365
ISO weeks: 52
Started on: Monday
January 1, 91
Ended on: Monday
December 31, 91
Friday the 13ths: 2
2 Friday the 13ths this year.
Decade: 90s
90–99
Century: 1st century
1–100
Millennium: 1st millennium
1–1000
Years ago: 1,935
1935 years before 2026.

In other calendars

Hebrew: 3851 / 3852 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Metal zodiac:Rabbit
Sexagenary cycle position 28 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 634 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: 83 / 84 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 13 / 12 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 2
Digit sum: 10
Digit product: 9
Digital root: 1
Palindrome: No
Bit width: 7 bits
Reversed: 19
Flips to (rotate 180°): 16
Recamán's sequence: a(65) = 91
Square (n²): 8,281
Cube (n³): 753,571
Divisor count: 4
σ(n) — sum of divisors: 112
φ(n) — Euler's totient: 72
Sum of prime factors: 20

Primality

Prime factorization: 7 × 13

Nearest primes: 89 (−2) · 97 (+6)

Divisors & multiples

All divisors (4)

1 · 7 · 13 · 91

Aliquot sum (sum of proper divisors): 21

Factor pairs (a × b = 91)

1 × 91

7 × 13

First multiples

91 · 182 (double) · 273 · 364 · 455 · 546 · 637 · 728 · 819 · 910

Sums & aliquot sequence

As consecutive integers: 45 + 46 10 + 11 + … + 16 1 + 2 + … + 13

Aliquot sequence: 91 → 21 → 11 → 1 → 0 — terminates at zero

Representations

In words: ninety-one
Ordinal: 91st
Roman numeral: XCI
Binary: 1011011
Octal: 133
Hexadecimal: 0x5B
Base64: Ww==
One's complement: 164 (8-bit)

In other bases

ternary (3) 10101

quaternary (4) 1123

quinary (5) 331

senary (6) 231

septenary (7) 160

nonary (9) 111

undecimal (11) 83

duodecimal (12) 77

tridecimal (13) 70

tetradecimal (14) 67

pentadecimal (15) 61

Historical numeral systems

Babylonian (base 60): 𒁹 𒌋𒌋𒌋𒁹
Egyptian hieroglyphic: 𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓏺
Greek (Milesian): ϟαʹ
Mayan (base 20): 𝋤·𝋫
Chinese: 九十一
Chinese (financial): 玖拾壹

In other modern scripts

Eastern Arabic ٩١ Devanagari ९१ Bengali ৯১ Tamil ௯௧ Thai ๙๑ Tibetan ༩༡ Khmer ៩១ Lao ໙໑ Burmese ၉၁

Digit at this position in famous constants

π — Pi (π): Digit 91 = 5
e — Euler's number (e): Digit 91 = 8
φ — Golden ratio (φ): Digit 91 = 4
√2 — Pythagoras's (√2): Digit 91 = 4
ln 2 — Natural log of 2: Digit 91 = 6
γ — Euler-Mascheroni (γ): Digit 91 = 3

Also seen as

ASCII character

As an ASCII codepoint, 91 is [. Printable ASCII character [.

Hex color

#00005B

RGB(0, 0, 91)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.91.

Address: 0.0.0.91
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.0.91

Unspecified address (0.0.0.0/8) — "this network" placeholder.

US numbered highway

Matches numbered highway designation:

I-91 — New Haven, CT to Derby Line, VT (Canadian border).

Interstate 91 on Wikipedia ↗