The Privileg PR-57NC is yet another European OEM copy of the classic Commodore PR-100: my first ever programmable calculator, the PTK-1072, was an identical machine, except that it was sold under a Hungarian OEM label.

A do-everything machine, the PR-57NC's main limitation is a completely unmerged programming model: every keystroke, including the F key and the (inv) key counts as separate keystrokes. This makes the calculator's 72-step program space more limited than necessary.

Back in the late 1970s, I found it a challenge to create an algorithm for this calculator that would compute the Gamma function. Today, I have several; one I developed just recently, based on an excellent suggestion I received from Robert H. Windschitl. With his empirical formula, it became possible to compute the Gamma function's logarithm to 8+ digits of precision, squeeze the algorithm, along with an iterative loop for small or negative arguments, into the PR-57NC's memory, and have some room to spare (specifically: 7 unused program steps.) My only wish now: a time machine with which I could send this result back to my younger self for his enjoyment (along with last week's lottery numbers of course.)

00	51	M
01	81	1
02	85	-
03	72	5
04	84	+
05	15	SKIP
06	14	GOTO
07	81	1
08	61	7
09	73	6
10	95	=
11	21	F
12	74	M×
13	81	1
14	14	GOTO
15	91	0
16	82	2
17	72	5
18	74	×
19	51	M
20	91	0
21	21	F
22	35	1/x
23	21	F
24	22	sinh
25	84	+
26	64	(
27	52	MR
28	91	0
29	34	yx
30	73	6
31	94	+/-
32	75	÷
33	62	8
34	81	1
35	91	0
36	95	=
37	35	√
38	74	×
39	52	MR
40	91	0
41	95	=
42	32	ln
43	74	×
44	52	MR
45	91	0
46	85	-
47	52	MR
48	91	0
49	84	+
50	64	(
51	82	2
52	74	×
53	45	π
54	74	×
55	52	MR
56	91	0
57	65	)
58	35	√
59	32	ln
60	85	-
61	52	MR
62	81	1
63	32	ln
64	95	=