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The label of an elliptic curve over a number field $K$ has three components, denoting the conductor, the isogeny class and the isomorphism class:

Together these give a label of the form $N.a1$ where $N$ is the conductor label, $a$ the class and $1$ the curve number.

In addition, to specify the elliptic curve completely prepend the label of the base field to give a full label of the curve, for example