OpenB@Side-PalmBack Flatten

Etymology
Similar handshape as with similar movement as the other number signs from  through.

Production

 * Flatten and extend the four fingers (not including the thumb) at least twice, keeping them together.
 * Flatten and extend the four fingers (not including the thumb) at least twice, keeping them together.
 * Flatten and extend the four fingers (not including the thumb) at least twice, keeping them together.

Number

 * 1) fifteen; 15