设为公差为d,则an=a1+(n-1)d依题意有a2+a3=a1+d+a1+2d =2a1+3d =13又a1=2,则3d=13-4=9,d=3那么，a4+a5+a6=a1+3d+a1+4d+a1+5d =3a1+12d =6+36 =42
