On peut faire beaucoup plus de 7 fonctions SI les unes dans les autres ou alors n'entendons pas "les unes dans les autres" de la même facon.
J'ai fais ce matin, dans une cellule, une fonction SI par semaine:
=SI(A35<=(DATE(2007; 1; 7));"semaine1";SI(A35<=(DATE(2007; 1; 14));"semaine2";SI(A35<=(DATE(2007; 1; 21));"semaine3";SI(A35<=(DATE(2007; 1; 28));"semaine4";SI(A35<=(DATE(2007; 2; 4));"semaine5";SI(A35<=(DATE(2007; 2;11));"semaine6";SI(A35<=(DATE(2007; 2; 18));"semaine7";SI(A35<=(DATE(2007; 2; 25));"semaine8";SI(A35<=(DATE(2007; 3; 4));"semaine9";SI(A35<=(DATE(2007; 3; 11));"semaine10";SI(A35<=(DATE(2007; 3; 18));"semaine11";SI(A35<=(DATE(2007; 3; 25));"semaine12";SI(A35<=(DATE(2007; 4; 1));"semaine13";SI(A35<=(DATE(2007; 4; 8));"semaine14";SI(A35<=(DATE(2007; 4; 15));"semaine15";SI(A35<=(DATE(2007; 4; 22));"semaine16";SI(A35<=(DATE(2007; 4; 29));"semaine17";SI(A35<=(DATE(2007; 5; 6));"semaine18";SI(A35<=(DATE(2007; 5; 13));"semaine19";SI(A35<=(DATE(2007; 5; 20));"semaine20";SI(A35<=(DATE(2007; 5; 27));"semaine21";SI(A35<=(DATE(2007; 6; 3));"semaine22";SI(A35<=(DATE(2007; 6; 10));"semaine23";SI(A35<=(DATE(2007; 6; 17));"semaine24";SI(A35<=(DATE(2007; 6; 24));"semaine25";SI(A35<=(DATE(2007; 7; 1));"semaine26";SI(A35<=(DATE(2007; 7; 8));"semaine27";SI(A35<=(DATE(2007; 7; 15));"semaine28";SI(A35<=(DATE(2007; 7; 22));"semaine29";SI(A35<=(DATE(2007; 7; 29));"semaine30";SI(A35<=(DATE(2007; 8; 5));"semaine31";SI(A35<=(DATE(2007; 8; 12));"semaine32";SI(A35<=(DATE(2007; 8; 19));"semaine33";SI(A35<=(DATE(2007; 8; 26));"semaine34";SI(A35<=(DATE(2007; 9; 2));"semaine35";SI(A35<=(DATE(2007; 9; 9));"semaine36";SI(A35<=(DATE(2007; 9; 16));"semaine37";SI(A35<=(DATE(2007; 9; 23));"semaine38";SI(A35<=(DATE(2007; 9; 30));"semaine39";SI(A35<=(DATE(2007; 10; 7));"semaine40";SI(A35<=(DATE(2007; 10; 14));"semaine41";SI(A35<=(DATE(2007; 10; 21));"semaine42";SI(A35<=(DATE(2007; 10; 28));"semaine43";SI(A35<=(DATE(2007; 11; 4));"semaine44";SI(A35<=(DATE(2007; 11; 11));"semaine45";SI(A35<=(DATE(2007; 11; 18));"semaine46";SI(A35<=(DATE(2007; 11; 25));"semaine47";SI(A35<=(DATE(2007; 12; 2));"semaine48";SI(A35<=(DATE(2007; 12; 9));"semaine49";SI(A35<=(DATE(2007; 12; 16));"semaine50";SI(A35<=(DATE(2007; 12; 23));"semaine51";SI(A35<=(DATE(2007; 12; 30));"semaine52";SI(A35<=(DATE(2007; 12; 31));"semaine53";213))))))))))))))))))))))))))))))))))))))))))))))))))))) &" 2007"