78
78 is a composite number, even, a calendar year.
78 (seventy-eight) is an even 2-digit number. It is a composite number with 8 divisors, and factors as 2 × 3 × 13. Its proper divisors sum to 90, more than the number itself, making it an abundant number. It is the twelfth triangular number. Written other ways, in Roman numerals it is LXXVIII and in binary, 1001110.
Interestingness
Historical context — 78 AD
Calendar year
AD 78 (LXXVIII) was a common year starting on Thursday of the Julian calendar.
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Historical context — 78 BC
Calendar year
Year 78 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, 78
- Ended on
-
Saturday
December 31, 78
- Friday the 13ths
-
1
One Friday the 13th this year.
- Decade
-
70s
70–79
- Century
-
1st century
1–100
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,948
1948 years before 2026.
In other calendars
- Hebrew
-
3838 / 3839 AM
Rosh Hashanah falls in September/October.
- Chinese
-
Year of the zodiac:Earth zodiac:Tiger
Sexagenary cycle position 15 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
621 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
70 / 71 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
0 / -1 Saka
Indian national calendar; year starts in March.
Properties
Primality
Prime factorization: 2 × 3 × 13
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√78 = [8; (1, 4, 1, 16)]
Period length 4 — the block in parentheses repeats forever.
Representations
- In words
- seventy-eight
- Ordinal
- 78th
- Roman numeral
- LXXVIII
- Binary
- 1001110
- Octal
- 116
- Hexadecimal
- 0x4E
- Base64
- Tg==
- One's complement
- 177 (8-bit)
- Scientific notation
- 7.8 × 10¹
- As a duration
- 78 s = 1 minute, 18 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒁹 𒌋𒁹𒁹𒁹𒁹𒁹𒁹𒁹𒁹
- Egyptian hieroglyphic
- 𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓏺𓏺𓏺𓏺𓏺𓏺𓏺𓏺
- Greek (Milesian)
- οηʹ
- Mayan (base 20)
- 𝋣·𝋲
- Chinese
- 七十八
- Chinese (financial)
- 柒拾捌
Digit at this position in famous constants
- π — Pi (π)
- Digit 78 = 0
- e — Euler's number (e)
- Digit 78 = 4
- φ — Golden ratio (φ)
- Digit 78 = 0
- √2 — Pythagoras's (√2)
- Digit 78 = 0
- ln 2 — Natural log of 2
- Digit 78 = 9
- γ — Euler-Mascheroni (γ)
- Digit 78 = 6
Also seen as
Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 78, here are decompositions:
- 5 + 73 = 78
- 7 + 71 = 78
- 11 + 67 = 78
- 17 + 61 = 78
- 19 + 59 = 78
- 31 + 47 = 78
- 37 + 41 = 78
As an ASCII codepoint, 78 is N. Printable ASCII character N.
As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.78.
- Address
- 0.0.0.78
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.0.78
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Matches numbered highway designation:
- I-78 — Union Township, PA to Holland Tunnel, NYC.
Heard as a frequency, 78 Hz is closest to:
- Concert pitch (A4 = 440 Hz): D♯2 (77.8 Hz, +5¢)
- Scientific pitch (C4 = 256 Hz): D♯2 (76.1 Hz, +42¢)
- Baroque pitch (A4 = 415 Hz): E2 (77.7 Hz, +6¢)
As a MIDI note number, 78 is F♯5 (740 Hz at concert pitch).
On the periodic table, atomic number 78 is Platinum (Pt) — period 6.
Related reading
- Triangular numbers — 1, 3, 6, 10, 15 … the counting numbers stacked into triangles, and Gauss's famous shortcut for summing them.
- Babylonian numerals — The base-60 cuneiform system that gave us 60 minutes, 60 seconds, and 360°.