Rebutia weingartia trolli
(This plant comes in a 3.5" pot. You will receive a very similar plant to the one in the picture. It may or may not be blooming at the time of your purchase. The plant is shipped in its pot to prevent any damage to the roots).
Also known as Weingartia trolli, it is a heavy bloomer characterized by bright orange to orange-scarlet flowers.
Blooming season: The flowers are produced in early summer and remain open for five or six days.
Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz