Quasi-quantization of writhe in ideal knots

The values of writhe of the most tight conformations, found by the SONO algorithm, of all alternating prime knots with up to 10 crossings are analysed. The distribution of the writhe values is shown to be concentrated around the equally spaced levels. As predicted by Cerf and Stasiak the writhe quantum is shown to be close to the rational 4/7 value. The deviation of the writhe values from the n*(4/7) writhe levels scheme is analysed quantitatively. Consequences of the writhe quantization phenomenon are discussed.