%I #5 Mar 27 2020 09:05:17
%S 1,1,3,6,10,6,21,28,36,20,55,36,78,42,60,120,136,72,171,120,126,110,
%T 253,168,300,156,351,252,406,120,465,496,330,272,420,432,666,342,468,
%U 560,820,252,903,660,720,506,1081,720,1176,600,816,936,1378,702,1100,1176,1026,812,1711,720
%N a(1) = 1; thereafter a(n) = n * uphi(n) / 2.
%C The unitary version of A023896.
%F a(n) = (n/2) * Sum_{d|n, gcd(d, n/d) = 1} (-1)^omega(n/d) * (d + 1).
%t uphi[n_] := Times @@ (#[[1]]^#[[2]] - 1 & /@ FactorInteger[n]); a[1] = 1; a[n_] := n uphi[n]/2; Table[a[n], {n, 1, 60}]
%t a[n_] := (n/2) Sum[If[GCD[d, n/d] == 1, (-1)^PrimeNu[n/d] (d + 1), 0], {d, Divisors[n]}]; Table[a[n], {n, 1, 60}]
%Y Cf. A001221, A023896, A047994, A076479, A145388.
%K nonn
%O 1,3
%A _Ilya Gutkovskiy_, Mar 27 2020
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