Alphabetic positions of P, i, D, a, and y are: 16, 9, 1, 4, and 25.
Writing without spaces this becomes:
1694125
This a permutation of 1415926, and we all know that this corresponds to the 7 digits following the decimal point in the decimal approximation of pi (which is 3.1415926.....)
[EDIT] : I see! I misunderstood the question!! Steve Herman's response is accurate to the puzzle as it is posited!!
I answered the possible question: "What relation do letters of "Pi Day" have with Pi?"
Nice puzzle, MM!!
Edited on March 14, 2022, 8:02 am