code: public DataSetBuilder sequence(String column, IntFunction<?> step, int initial) {
      ensureArgNotNull(step);
      return set(column, new SequenceFiller(step, initial));
    }
docs: Set sequence filler using a index-based step-function.
  
  <p>
  The sequence of values generated by the filler starts
  with the specified initial value, and subsequent values
  are generated using the step function which takes as input the
  index of the row being generated, starting from the initial value.
  The sequence will then be
  <code>s(start), s(start+1), ...</code> where <code>s(i) = step.apply(i)</code>
  for all <code>i &gt;= start</code>.
  </p>
  
  @param column Column name.
  @param step Step function.
  @param initial Initial value fed to step function.
  @return The builder instance (for chained calls).
  @see #sequence(String, Object, UnaryOperator)