Fewest different prime factors Since no S-number is a power of 3, the theoretical minimum is 2 in the form [3.sup.m].[p.sup.n], as in B above or 735982641 = [3.sup.2].[9043.sup.2] (D1) or 185742639 = [3.sup.6].254791 (D2).
= 362880 ways, so that there are that many different S-numbers ranging from 123456789 = [3.sup.2].3607.3803 (A1) to 987654321 = [3.sup.2].[17.sup.2].379721 (A2).
Fewest prime factors The theoretical minimum of 3 is found for all S-numbers of form [3.sup.2].p.
Roundest numbers The seven roundest S-numbers I have found are:(i)
It will be seen that G2 is twice G1, and there are other pairs of S-numbers which are similarly closely related.
Squares Table 64 in Albert Beiler's "Recreations in the Theory of Numbers" (Dover, New York, 1966) lists 30 S-numbers which are perfect squares, including D1, F4 and G2 above.
Commonly recognized terms include the exposure index (EI) or sensitivity (S-number).
Fuji Medical System's CR unit provides a sensitivity value, an S-number, that is inversely proportional to the actual exposure to the imaging plate.
Manufacturers of CR equipment are beginning to address the potential problem of S-number variability.
As with the Fuji S-number, there is concern regarding the consistency of the exposure index.
Tolerance limits for S-number variability are not specifically addressed in the draft document, although the AAPM recommends that linearity of the reader response to the IP exposure should correlate within 10%.
The manufacturer does not provide an expected S-number when using the suggested technical factors.