Number sets in HTML and Unicode | Double-struck letters

When I started blogging I was very cautious about what characters I used because browsers often didn’t have font support for uncommon characters. Things have changed since then and I’ve gotten less cautious. Nobody has complained, so I assume readers are seeing the characters I intend them to see.

There are Unicode characters for sets of numbers such as the integers and the real numbers, double-struck letters similar to the blackboard bold letters \mathbb{Z} etc. in LaTeX.

$\mathbb{N} \quad \mathbb{Z} \quad \mathbb{Q} \quad \mathbb{R} \quad \mathbb{C} \quad \mathbb{H}$

Here’s a table of the characters, their Unicode values, and two HTML entities associated with each.

    ℕ U+2115 &Nopf; &naturals;
    ℤ U+2124 &Zopf; &integers;
    ℚ U+211A &Qopf; &rationals;
    ℝ U+211D &Ropf; &reals;
    ℂ U+2102 &Copf; &complexes;
    ℍ U+210D &Hopf; &quaternions;

If you’re going to use these symbols, you will likely also need to use ∈ (U+2208, &in;) and ∉ (U+2209, ∉).

More letters

If you want more letters in the style of those above, you can find them starting at U+1D538 for . However, the characters corresponding to letters above are reserved.

So for example, is U+1D538, is U+1D539, but U+1D53A is reserved and you must use ℂ (U+2102) instead.

One letter not mentioned above is ℙ (U+2119). It has HTML entities &Popf; and &primes;.

So the double-struck versions of C, H, N, P, Q, R, and Z are down in the BMP (Basic Multilingual Plane) and the rest are in the SMP (Supplementary Multilingual Plane). I suspect characters in the SMP are less likely to have font support, but that may not be a problem.