A126578 a(n) = denominator of the sum of reciprocals of the terms in n-th row of triangle A077581.
1, 3, 4, 105, 4, 85085, 40, 45045, 40040, 66927861, 2520, 167133741775, 27720, 644658718275, 16997552, 4512611027925, 240240, 190103424450275260925, 816816, 3873805630307495883, 28269478608800, 1257729100749186975, 15519504
Offset: 1
Examples
Row 4 of triangle A077581 is (1,3,5,7). So a(4) is the denominator of 1/1 +1/3 +1/5 + 1/7 = 176/105.
Programs
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Mathematica
row[n_] := Take[Select[Range[n^2], GCD[ #, n] == 1 &], n]; Table[Denominator[Plus @@ (1/# &) /@ row[n]], {n, 23}] (* Ray Chandler, Dec 29 2006 *)
Extensions
Extended by Ray Chandler, Dec 29 2006