An isosceles triangle has two equal sides only.
The prime numbers are 2, 3, 5, 7, 11. We don’t whether the prime sides are equal, but let’s assume that they are. So we could have 2×2+21, 2×3+19 (all 3 sides are prime), 2×5+15, 2×7+11 (all sides prime), 2×11+3 (all sides prime). These are all possible integer values (measurements in cm).