units transformation problem

[abchaoming1]

Dear develpers:

I really do not figure out what the transformation relation between the THz and cm-1,because I think the transformation of THz to cm-1 is 33.35641 and the units factor in phonopy is 15.633302 which is phonopy default factor value.
But I tried so much times and the result of factor comes out is 33.35641*7.

Best regards;
Haoming Zhang