Let phi = arccos(1/3), the dihedral angle of the regular tetrahedron. Then cos(n*phi) = a(n)/3^n.

A025172

Let phi = arccos(1/3), the dihedral angle of the regular tetrahedron. Then cos(n*phi) = a(n)/3^n.

Terms

    a(0) =1a(1) =1a(2) =-7a(3) =-23a(4) =17a(5) =241a(6) =329a(7) =-1511a(8) =-5983a(9) =1633a(10) =57113a(11) =99529a(12) =-314959a(13) =-1525679a(14) =-216727a(15) =13297657a(16) =28545857a(17) =-62587199a(18) =-382087111a(19) =-200889431a(20) =3037005137a(21) =7882015153a(22) =-11569015927a(23) =-94076168231a(24) =-84031193119a(25) =678623127841

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