countable set
set with the same cardinality as some subset of the set of natural numbers
MathWorld: CountableSetWikipedia (English): Countable_set
ProofWiki: Definition:Countable_Set
Wikidata: countable set
mathswitch — infrastructure for relaying and exchanging mathematical concepts
set with the same cardinality as some subset of the set of natural numbers
MathWorld: CountableSet