We have,
x−12−x−21=k2
⇒(x−1)(x−2)2x−4−x+1=k2
⇒x2−3x+2x−3=k2
⇒kx−3k=2x2−6x+4
⇒2x2−(6+k)x+3k+4=0
For no real roots D<0
⇒(6+k)2−8(3k+4)<0
⇒k2+12k+36−24k−32<0
⇒(k−6)2−32<0
⇒∣k−6∣<32
⇒6−32<k<6+32
Integral value of k=1,2,3,4,5,6,7,8,9,10,11
Sum=211×12=66