How can I find the fulfillment order number in the REST API?

[RedYellowBlue]

Hi, 

I'm using the REST API. I developed an order management app and a fulfillment service. 

My users see 1234-F1 in Shopify when I fulfill a fulfillment order. I would like to use this order number or fulfillment number as well, but the only thing I get from the API are long id's. I can nowhere find if my fulfilment order is the first or the second fulfillment order within an order.