Serial number 525540, 1959-1960 version, this lens has 9 aperture blades, instead of 6 blades in later Nikkor-S lens with serial number 53xxxx.  According to Nikon database, 5cm f/2 tick mark lenses have serial numbers from 520101 to 525981.  This particular lens with serial number 525540 has no tick marks and thus is a very rare exception!

This lens is in overall excellent condition, except a tiny dent in the front side (see photo #7) which does not affect any function at all.  The glass is clean and free of fungi or scratch.  The aperture ring clicks crisply and the focusing is smooth.  A 100% functional lens.