a:23=c rest 1
a=23c+1
a-1=23c+1-1
a-1=23c
a-1∈M[23]
M[23]={23,46,69,92,115, 138....989}⇒obs.989=23·43
a-1=115
a=115+1
a=116
116:23=5 rest 1
a-1=138
a=138+1
a=139
139:23=6
deci nr.115+1, 138+1.......989+1 impartite la 23 dau restul 1
pt.ca sunt 43nr.-4nr=39 nr.cor indeplini cond.enuntata