Number

61

61 is a prime, odd, a calendar year.

Arithmetic Number Deficient Number Flippable Keith Number Odious Number Pernicious Number Prime Pythagorean Prime Recamán's Sequence Sexy Prime Squarefree Twin Prime Year

Historical context — 61 AD

Calendar year

AD 61 (LXI) was a common year starting on Thursday of the Julian calendar.

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Historical context — 61 BC

Calendar year

Year 61 BC was a year of the pre-Julian Roman calendar.

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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: Saturday
January 1, 61
Ended on: Saturday
December 31, 61
Friday the 13ths: 1
One Friday the 13th this year.
Decade: 60s
60–69
Century: 1st century
1–100
Millennium: 1st millennium
1–1000
Years ago: 1,965
1965 years before 2026.

In other calendars

Hebrew: 3821 / 3822 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Metal zodiac:Rooster
Sexagenary cycle position 58 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 604 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: 53 / 54 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): -17 / -18 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 2
Digit sum: 7
Digit product: 6
Digital root: 7
Palindrome: No
Bit width: 6 bits
Reversed: 16
Flips to (rotate 180°): 19
Recamán's sequence: a(181,653) = 61
Square (n²): 3,721
Cube (n³): 226,981
Divisor count: 2
σ(n) — sum of divisors: 62
φ(n) — Euler's totient: 60

Primality

61 is prime. It has exactly two divisors: 1 and itself.

Divisors & multiples

All divisors (2)

1 · 61

Aliquot sum (sum of proper divisors): 1

Factor pairs (a × b = 61)

1 × 61

First multiples

61 · 122 (double) · 183 · 244 · 305 · 366 · 427 · 488 · 549 · 610

Sums & aliquot sequence

As a sum of two squares: 5² + 6²

As consecutive integers: 30 + 31

Representations

In words: sixty-one
Ordinal: 61st
Roman numeral: LXI
Binary: 111101
Octal: 75
Hexadecimal: 0x3D
Base64: PQ==
One's complement: 194 (8-bit)

In other bases

ternary (3) 2021

quaternary (4) 331

quinary (5) 221

senary (6) 141

septenary (7) 115

nonary (9) 67

undecimal (11) 56

duodecimal (12) 51

tridecimal (13) 49

tetradecimal (14) 45

pentadecimal (15) 41

Historical numeral systems

Babylonian (base 60): 𒁹 𒁹
Egyptian hieroglyphic: 𓎆𓎆𓎆𓎆𓎆𓎆𓏺
Greek (Milesian): ξαʹ
Mayan (base 20): 𝋣·𝋡
Chinese: 六十一
Chinese (financial): 陸拾壹

In other modern scripts

Eastern Arabic ٦١ Devanagari ६१ Bengali ৬১ Tamil ௬௧ Thai ๖๑ Tibetan ༦༡ Khmer ៦១ Lao ໖໑ Burmese ၆၁

Digit at this position in famous constants

π — Pi (π): Digit 61 = 4
e — Euler's number (e): Digit 61 = 7
φ — Golden ratio (φ): Digit 61 = 8
√2 — Pythagoras's (√2): Digit 61 = 9
ln 2 — Natural log of 2: Digit 61 = 0
γ — Euler-Mascheroni (γ): Digit 61 = 7

Also seen as

Prime neighborhood

Adjacent primes:

Previous prime: 59 (gap of 2)
Next prime: 67 (gap of 6)

Pair status: twin with 59, sexy with 67.

ASCII character

As an ASCII codepoint, 61 is =. Printable ASCII character =.

Hex color

#00003D

RGB(0, 0, 61)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.61.

Address: 0.0.0.61
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.0.61

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