<h1 id="closed-formula">Closed Formula<a aria-hidden="true" class="anchor-heading icon-link" href="#closed-formula"></a></h1>
A closed formula is one that doesn't contain a <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo>∑</mo></mrow><annotation encoding="application/x-tex">\sum</annotation></semantics></math>∑ or <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo>∏</mo></mrow><annotation encoding="application/x-tex">\prod</annotation></semantics></math>∏.
Example:
<div class="math math-display"><math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><semantics><mrow><msub><mi>a</mi><mi>n</mi></msub><mo>=</mo><mfrac><mrow><msup><mn>3</mn><mi>n</mi></msup><mo>−</mo><mn>1</mn></mrow><mi>n</mi></mfrac></mrow><annotation encoding="application/x-tex">a_n = \frac{3^n - 1}{n}</annotation></semantics></math>an​=n3n−1​</div>
A closed formula can have a the sum or product of a fixed number of parts, but not a changing number of parts.

Closed Formula


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