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a(n) = denominator of the sum of reciprocals of the terms in n-th row of triangle A077581.
1

%I #10 Oct 10 2019 13:45:44

%S 1,3,4,105,4,85085,40,45045,40040,66927861,2520,167133741775,27720,

%T 644658718275,16997552,4512611027925,240240,190103424450275260925,

%U 816816,3873805630307495883,28269478608800,1257729100749186975,15519504

%N a(n) = denominator of the sum of reciprocals of the terms in n-th row of triangle A077581.

%e Row 4 of triangle A077581 is (1,3,5,7).

%e So a(4) is the denominator of 1/1 +1/3 +1/5 + 1/7 = 176/105.

%t row[n_] := Take[Select[Range[n^2], GCD[ #, n] == 1 &], n]; Table[Denominator[Plus @@ (1/# &) /@ row[n]], {n, 23}] (* _Ray Chandler_, Dec 29 2006 *)

%Y Cf. A077581, A126577.

%K frac,nonn

%O 1,2

%A _Leroy Quet_, Dec 28 2006

%E Extended by _Ray Chandler_, Dec 29 2006