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a(n) = (n+1)*phi(n-1)/2.
1

%I #11 Sep 18 2017 12:11:07

%S 2,5,6,14,8,27,20,33,24,65,28,90,48,68,72,152,60,189,88,138,120,275,

%T 104,270,168,261,180,434,128,495,272,350,288,444,228,702,360,492,336,

%U 860,264,945,460,564,528,1127,400,1071,520,848,648,1430,504,1140,696,1062,840,1769

%N a(n) = (n+1)*phi(n-1)/2.

%C The old entry with this sequence number was a duplicate of A082470.

%H J. Jaffe, <a href="http://www.jstor.org/stable/2689434">Permutation numbers</a>, Math. Mag., 49 (1976), 80-84.

%t Table[(n+1) EulerPhi[n-1]/2,{n,3,60}] (* _Harvey P. Dale_, Apr 22 2012 *)

%o (PARI) a(n) = (n+1)*eulerphi(n-1)/2; \\ _Michel Marcus_, Sep 18 2017

%K nonn

%O 3,1

%A _N. J. A. Sloane_, Nov 04 2008