A064485 - OEIS

A064485

Number of ordered pairs a,b of elements in the dihedral group D_2n such that the subgroup generated by the pair a,b is a proper subgroup of D_2n.

%I #7 Oct 09 2014 16:37:45

%S 1,10,18,40,40,108,70,160,162,280,154,432,208,532,540,640,340,972,418,

%T 1120,1008,1276,598,1728,1000,1768,1458,2128,928,2880,1054,2560,2376,

%U 2992,2380,3888,1480,3724,3276,4480,1804,5544,1978,5104,4860,5428,2350,6912

%N Number of ordered pairs a,b of elements in the dihedral group D_2n such that the subgroup generated by the pair a,b is a proper subgroup of D_2n.

%F a(n) = 4*n^2 - A064400(n) = 4*n^2 - 3*n*phi(n).

%p with(numtheory): A064485:=n->4*n^2-3*n*phi(n): seq(A064485(n), n=1..50); # _Wesley Ivan Hurt_, Oct 08 2014

%t Table[4 n^2 - 3 n*EulerPhi[n], {n, 50}] (* _Wesley Ivan Hurt_, Oct 08 2014 *)

%Y Cf. A064400, A064279.

%K nonn

%O 1,2

%A Dan Fux (dan.fux(AT)OpenGaia.com or danfux(AT)OpenGaia.com), Oct 03 2001

%E More terms from _Eric M. Schmidt_, Oct 08 2014