Math 2.0

Sequences, series, summability Definition

Sequence

Definition

Let XX be a set. A sequence in XX is a function a ⁣:ℕ→Xa \colon \mathbb{N} \to X, where ℕ={0,1,2,… }\mathbb{N} = \{0, 1, 2, \dots\}. The value a(n)a(n) is the nn-th term of the sequence, with the notation ana_n. The notation for the sequence is (an)n∈ℕ(a_n)_{n \in \mathbb{N}}, or (an)(a_n) when the index set is clear.

Remarks

Many texts start the index at 11, and they use a function on {1,2,3,… }\{1, 2, 3, \dots\}. The theory does not change. The terms of a sequence can repeat. For example, (1,0,1,0,… )(1, 0, 1, 0, \dots) is the sequence with an=1a_n = 1 for even nn and an=0a_n = 0 for odd nn. A sequence of real numbers is a real sequence.

Where this leads

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Further reading

  1. Web https://en.wikipedia.org/wiki/Sequence, Formal definition and basic properties
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