Algebra
Infinite series
Sums that go on forever — and the surprising ones that still settle on a number.
A sum of infinitely many terms. Sometimes it converges to a number, sometimes it diverges.
1 + 1/2 + 1/4 + 1/8 + ... = 2. But 1 + 1/2 + 1/3 + 1/4 + ... = ∞ (the harmonic series diverges).