C ( v ) = 2 | ∪ i , j ∈ N ( v )   ( i , j )    |   d ( v ) ( d ( v ) − 1 )         ( 4 )    MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=vr0dc8meaabaqaciaacaGaaeqabaqabeGadaaakeaacqWGdbWqcqGGOaakcqWG2bGDcqGGPaqkcqGH9aqpdaWcaaqaaiabikdaYmaaemaabaWaambeaeaacqGGOaakcqWGPbqAcqGGSaalcqWGQbGAcqGGPaqkaSqaaiabdMgaPjabcYcaSiabdQgaQjabgIGiolabd6eaojabcIcaOiabdAha2jabcMcaPaqab0GaeSOkIufaaOGaay5bSlaawIa7aaqaaiabdsgaKjabcIcaOiabdAha2jabcMcaPiabcIcaOiabdsgaKjabcIcaOiabdAha2jabcMcaPiabgkHiTiabigdaXiabcMcaPaaacaWLjaGaaCzcamaabmaabaGaeGinaqdacaGLOaGaayzkaaaaaa@567E@