Double-struck n-ary summation (⅀) is the Unicode character at U+2140 in the Letterlike Symbols block. Official name: DOUBLE-STRUCK N-ARY SUMMATION (also called blackboard bold summation). It is used in mathematical and scientific notation for series / sums.
Remember
Character ⅀
Unicode U+2140
Hex entity ⅀
Decimal ⅀
CSS escape \2140
Named entity (none)
Not the same ∑ (∑)
Prefer ⅀ or ⅀ in HTML (no named form). You can also type ⅀ in UTF-8.
Double-struck sum using Hex Code: ⅀
Double-struck sum using HTML Code: ⅀
Double-struck sum using CSS Entity: ⅀
Typed directly: ⅀
Compared: ⅀ (double-struck) vs ∑ (ordinary)
How It Works
1. Hex:U+2140 → ⅀ in HTML. Preferred when there is no named entity.
2. Decimal: same code point as 8512 → ⅀. Same result as hex.
3. CSS: use \2140 in content (not an HTML entity). #point::after appends that ⅀ after the paragraph text.
4. Typed / compared: paste ⅀ in UTF-8, or contrast it with ∑ (∑).
Pitfalls & Tips
Common mistakes when working with Double Struck N-Ary Summation.
Name
No named entity
There is no HTML5 named entity for U+2140. Use ⅀ or ⅀.
∑
Not ∑
∑ is ordinary n-ary summation (U+2211). Double-struck summation is a different Letterlike Symbol.
Default
Prefer ∑ for everyday sums
For most formulas, use ∑. Reserve U+2140 when you specifically need the blackboard-bold look.
CSS vs HTML
Do not mix escapes
\2140 belongs in CSS strings. ⅀ / ⅀ belong in HTML.
Fonts
Math font coverage
Some fonts omit Letterlike Symbols. Prefer a math-capable font for reliable display of ⅀.
Semicolon
End references
Always finish numeric entities with ; — write ⅀, not ⅀.
Compatibility
Browser Support
Double-struck n-ary summation (U+2140) and its entity forms (⅀, ⅀, CSS \\2140) are supported in all mainstream browsers. Visible glyphs depend on math / Letterlike Symbols font coverage.
✓ Universal support
Double Struck N-Ary Summation (⅀)
Encode with hex, decimal, CSS escape, or type the character — same code point everywhere encoding is supported.
100%Browser coverage
Google ChromeSupported
Yes
Microsoft EdgeSupported
Yes
Mozilla FirefoxSupported
Yes
Apple SafariSupported
Yes
OperaSupported
Yes
Internet ExplorerAll versions
Yes
U+2140 / entitiesFull support
Bottom line: Prefer ⅀ in HTML (no named form). Use ⅀ when decimal form is required, and \\2140 only inside CSS content.
HTML: no named entity — use ⅀ / ⅀ / type ⅀.
CSS: use \2140 inside content for generated text.
Meaning:⅀ = blackboard-bold summation — not ∑ (∑).
One line:U+2140 → ⅀ / ⅀ / CSS \2140 / type ⅀.
Frequently Asked Questions
Use ⅀ (hex), ⅀ (decimal), type ⅀ directly in UTF-8, or the CSS escape \2140 in content. There is no named HTML entity for U+2140.
U+2140 (DOUBLE-STRUCK N-ARY SUMMATION). Hex 2140, decimal 8512. It belongs to the Letterlike Symbols block (U+2100–U+214F).
No. Use numeric forms ⅀ or ⅀, or type the character in a UTF-8 document. Ordinary summation uses ∑ (U+2211) — a different character.
Use it in mathematical or scientific text when you need the blackboard-bold / double-struck summation glyph. Prefer ∑ for the ordinary n-ary summation operator ∑.
HTML entities (⅀ or ⅀) go in markup. The CSS escape \2140 goes in stylesheet strings (usually content on ::before/::after).
No. U+2140 is double-struck n-ary summation ⅀. ∑ is n-ary summation ∑ (U+2211) — the standard sigma-style sum operator.
🤔
Did you know?
Double-struck n-ary summation is Unicode U+2140 (decimal 8512) — glyph ⅀ in the Letterlike Symbols block. There is no HTML5 named entity; use ⅀ or ⅀. Also called blackboard bold summation. Do not confuse with ordinary n-ary summation ∑ (∑, U+2211).
