Fewest different prime factors Since no S-number is a power of 3, the theoretical minimum is 2 in the form [3.
The largest prime whose square divides a S-number is 9043 in D1 above.
362880 ways, so that there are that many different S-numbers ranging from 123456789 = [3.
Fewest prime factors The theoretical minimum of 3 is found for all S-numbers of form [3.
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.