The value of p for which vectors i +2 j +3 k and 2 i - p j + k are perpendicular to each other is

The value of p for which vectors $\displaystyle \hat{\mathrm{i}}+2 \hat{\mathrm{j}}+3 \hat{\mathrm{k}}$ and $\displaystyle 2 \hat{\mathrm{i}}-\mathrm{p} \hat{\mathrm{j}}+\hat{\mathrm{k}}$ are perpendicular to each other is