"Counting in their heads"  1895 oil painting

08092020, 08:11 PM
Post: #7




RE: "Counting in their heads"  1895 oil painting
Alternatively, you can use this formula:
n[c + (n²  1)/12] where n is the number of elements in the sequence and c is the central element. 5[12² + (5²  1)/12] = 5[144 + 2] = 730 This should work also for sequences with even number of elements. For instance, 5² + 6² + 7² + 8² = 4[6.5² + (4²  1)/12] = 174 A bit more difficult to do it in one’s head, though. 

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