HP 15C Combination Curiosity (bug?)

[Eddie W. Shore]

Let: R1 = 45, R2 = 5, R3 = 3

Problem 1:

COMB(R1, R2) + COMB(R1, R3)

Code:

Code:

LBL A 
RCL 1
RCL 2
Cy,x
RCL 1
RCL 3 
Cy,x 
+
RTN

HP 15C Collector's Edition: 1,235,949 (no flash)
HP 15C Limited Edition: 1,235,949 (no flash)
HP 11C: 1,235,949 (no flash)

Problem 2:

COMB(R1, R2) × COMB(R1, R3)

Code:

Code:

LBL B 
RCL 1
RCL 2
Cy,x
RCL 1
RCL 3 
Cy,x 
×
RTN

HP 15C Collector's Edition: 1.7337e10 (no flash)
HP 15C Limited Edition: 1.7337e10 (no flash)
HP 11C: 1.7337e10 (no flash)

Problem 3:

COMB(R2, R3) × COMB(R1 - R2, R2 - R3) ÷ COMB(R1, R2)

Code:

Code:

LBL C
RCL 2
RCL 3
Cy,x
RCL 1 
RCL 2 
-
RCL 2
RCL 3 
- 
Cy,x
×
RCL 1
RCL 2 
Cy,x
÷
RTN

HP 15C Collector's Edition: 0.0006 (flashes)
HP 15C Limited Edition: 0.0064 (flashes)
HP 11C: 0.0006 (no flash)
(similar test on a HP 32SII: 0.0064 (no overflow error))


Problem 4:

COMB(R1, R2) ÷ COMB(R2, R3)

Code:

Code:

LBL D
RCL 1
RCL 2
Cy,x
RCL 2
RCL 3 
Cy,x 
÷
RTN

HP 15C Collector's Edition: 122,175.9 (no flash)
HP 15C Limited Edition: 122,175.9 (no flash)
HP 11C: 122,175.9 (no flash)


Problem 5: Same as problem 3 but store R4 = R1 - R2, R5 = R2 - R3

LBL E

Code:

RCL 1
RCL 2
-
STO 4
RCL 2
RCL 3
- 
STO 5
RCL 2
RCL 3
Cy,x
RCL 4 
RCL 5 
Cy,x
×
RCL 1
RCL 2 
Cy,x
÷
RTN

HP 15C Collector's Edition: 0.0064 (flashes)
HP 15C Limited Edition: 0.0064 (flashes)
(work around did not appear to work)
HP 11C: 0.0064 (no flash)


HP 15C: I don't know what causes the display to flash on problem 3 and 5. When I enter the key strokes manually, I don't get the flashes.

HP 15C Collector's Edition: 00935 (2023 - Philippines)
HP 15C Limited Edition: 01535 (2011 - China)
HP 11C: Serial # 2416A74279 (USA)