[seqfan] A061857

israel at math.ubc.ca israel at math.ubc.ca
Mon May 7 22:35:07 CEST 2012

A061857 was just now referenced in math.stackexchange.com


This is described as "Triangle where the k-th item at n-th row (both 
starting from 1) tells in how many ways we can add 2 distinct integers from 
1 to n, in such way that the sum is divisible by k."

Since the sum of two distinct integers from 1 to n can be as much as 2n-1,
I don't see why the n'th row shouldn't have 2n-1 entries.
But in fact the n'th row of the table has only n entries.
Thus e.g. the 6th row is given as 
15, 6, 5, 3, 3, 2
but I think it should be 
15, 6, 5, 3, 3, 2, 3, 2, 2, 1, 1

Robert Israel
University of British Columbia

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