Question 115576
a + (n-1)d + half(n-1)(n-2)c 
a = value of first term in sequence
d = first difference between the first two numbers
c = is the change between one difference and the next 
a = 481
d = 600
c = 240 
Changing Difference Sequence:

481, 1081, 1921, 3001, 4321 Sequence
600 840 1080 1320 first difference
240 240 240 Second difference 
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changing difference = 481+(5-1)600 + (1/2)(5-1)(5-2)240
cd = 481 + 2400 + 6*240
cd = 4321
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Comment: I've never heard of this "changing difference", but if your
formulas and numbers are correct 4321 is the result.  
Question: What does cd=4321 tell you?
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Cheers,
Stan H.