#Python, <s>80</s> 73 bytes

First submission, don't be too harsh q:

0-indexed

    lambda x,y:[(a-1,b//a,b%a)for a in range(25)for b in range(a**2)][70*x+y]

Creates a list of length 4900 with all pyramind coordinates and returns a different list entry for each input.

<a href="https://tio.run/##K6gsycjPM/7/PycxNyklUaFCp9IqWiNR11AnSV8/USdJNVEzLb9IIVEhM0@hKDEvPVXDyBQskoQQSdTSMtKMjTY30KrQroz9n2Ybw0U107gKijLzSjTSNMx0LDQ1////DwA" title="Python 3 – Try It Online">Try it online!</a>