61
61 is a prime, odd, a calendar year.
61 (sixty-one) is an odd 2-digit number. It is a prime number — divisible only by 1 and itself. Written other ways, in Roman numerals it is LXI and in binary, 111101.
Interestingness
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
Primality
61 is prime. It has exactly two divisors: 1 and itself.
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√61 = [7; (1, 4, 3, 1, 2, 2, 1, 3, 4, 1, 14)]
Period length 11 — the block in parentheses repeats forever.
Representations
- In words
- sixty-one
- Ordinal
- 61st
- Roman numeral
- LXI
- Binary
- 111101
- Octal
- 75
- Hexadecimal
- 0x3D
- Base64
- PQ==
- One's complement
- 194 (8-bit)
- Scientific notation
- 6.1 × 10¹
- As a duration
- 61 s = 1 minute, 1 second
As an angle
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
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
As an ASCII codepoint, 61 is =. Printable ASCII character =.
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.
Heard as a frequency, 61 Hz is closest to:
- Concert pitch (A4 = 440 Hz): B1 (61.7 Hz, -21¢)
- Scientific pitch (C4 = 256 Hz): B1 (60.4 Hz, +17¢)
- Baroque pitch (A4 = 415 Hz): C2 (61.7 Hz, -19¢)
As a MIDI note number, 61 is C♯4 (277.2 Hz at concert pitch).
On the periodic table, atomic number 61 is Promethium (Pm) — period 6.
Related reading
- Prime numbers — The building blocks of arithmetic: what primes are, why they matter, and how we find them.
- Egyptian hieroglyphic numerals — Seven hieroglyphs for every power of ten, from a single stroke to a million.