EntityQ1707307· pop 13· linked from 227 articlesfriendly numberSign in to savenatural number sharing its abundancy index with at least one other numberConnectionsprime numberEntityperfect numberEntityamicable numbersEntityfigurate numberEntitysociable numberEntityautomorphic numberEntitynatural numberEntitynumber theoryEntityrational numberEntitydigital object identifierEntitybinary numeral systemEntitydigitEntityInternational Standard Serial NumberEntityexponentiationEntitynumeral systemEntitygreatest common divisorEntitythree-dimensional spaceEntityparityEntitynatural languageEntitycomposite numberEntityCategoriesDivisor functionInteger sequencesUnsolved problems in number theory