=NO.SEMAINE(DATE)
=ENT((A1-SOMME(MOD(DATE(ANNEE(A1-MOD(A1-2;7)+3);1;2);{1E+99;7})*{1;-1})+5)/7)
[COLOR=green]' D correspondant à la date désirée[/COLOR]
Function NOSEM(D As Date) As Long
D = Int(D)
NOSEM = DateSerial(Year(D + (8 - WeekDay(D)) Mod 7 - 3), 1, 1)
NOSEM = ((D - NOSEM - 3 + (WeekDay(NOSEM) + 1) Mod 7)) \ 7 + 1
End Function