Take a number z of x digits and consider any concatenation z = concat(y_1, y_2, ..., y_i) where y_1, y_2, ..., y_i have the same number of digits. Then be g(z) the product of the sums y_1 + y_2 + ... + y_i for all those concatenations. Sequence lists numbers z such that g(g(z)) = z. (See example.)

A317628

Take a number z of x digits and consider any concatenation z = concat(y_1, y_2, ..., y_i) where y_1, y_2, ..., y_i have the same number of digits. Then be g(z) the product of the sums y_1 + y_2 + ... + y_i for all those concatenations. Sequence lists numbers z such that g(g(z)) = z. (See example.)