Character table for the D₇ point group

D7      E       2 C7    2 C7^2  2 C7^3  7 C2'      <R> <p> <—d—> <——f——> <———g———> <————h————> <—————i—————> 
A1      1.0000  1.0000  1.0000  1.0000  1.0000     ... ... ....T ....... ........T ........... ............T
A2      1.0000  1.0000  1.0000  1.0000 -1.0000     ..T ..T ..... ......T ......... ..........T .............
E1      2.0000  1.2469 -0.4450 -1.8019  0.0000     TT. TT. ..TT. ....TT. ......TT. ........TT. TT........TT.
E2      2.0000 -0.4450 -1.8019  1.2469  0.0000     ... ... TT... ..TT... ....TT... TT....TT... ..TT....TT...
E3      2.0000 -1.8019  1.2469 -0.4450  0.0000     ... ... ..... TT..... TTTT..... ..TTTT..... ....TTTT.....

 Irrational character values:  1.246979603717 = 2*cos(2*π/7)
                              -0.445041867913 = 2*cos(4*π/7)
                              -1.801937735805 = 2*cos(6*π/7)



 Symmetry of Rotations and Cartesian products

A1   d+g+i+j+2k+l+2m             z2, z4, z6 
A2   R+p+f+h+2j+k+2l+m           Rz, z, z3, z5 
E1   R+p+d+f+g+h+2i+2j+3k+3l+3m  {Rx, Ry}, {x, y}, {xz, yz}, {xz2, yz2}, {xz3, yz3}, {xz4, yz4}, {x2(x2−3y2)2−y2(3x2−y2)2, xy(x2−3y2)(3x2−y2)}, {xz5, yz5} 
E2   d+f+g+2h+2i+2j+2k+3l+3m     {x2−y2, xy}, {z(x2−y2), xyz}, {z2(x2−y2), xyz2}, {x(x2−(5+2√5)y2)(x2−(5−2√5)y2), y((5+2√5)x2−y2)((5−2√5)x2−y2)}, {z3(x2−y2), xyz3}, {xz(x2−(5+2√5)y2)(x2−(5−2√5)y2), yz((5+2√5)x2−y2)((5−2√5)x2−y2)}, {z4(x2−y2), xyz4} 
E3   f+2g+2h+2i+2j+2k+2l+3m      {x(x2−3y2), y(3x2−y2)}, {(x2−y2)2−4x2y2, xy(x2−y2)}, {xz(x2−3y2), yz(3x2−y2)}, {z((x2−y2)2−4x2y2), xyz(x2−y2)}, {xz2(x2−3y2), yz2(3x2−y2)}, {z2((x2−y2)2−4x2y2), xyz2(x2−y2)}, {xz3(x2−3y2), yz3(3x2−y2)} 

 Notes:

    α  The order of the D7 point group is 14, and the order of the principal axis (C7) is 7. The group has 5 irreducible representations.

    β  The D7 point group is isomorphic to C7v.

    γ  The D7 point group is generated by two symmetry elements, C7 and a perpendicular C2′.
       Also, the group may be generated from any two C2′ axes.

    δ  The group contains one set of C2′ symmetry axes perpendicular to the principal (z) axis. The x axis (but not the y axis) is a member of that set.

    ε  The lowest nonvanishing multipole moment in D7 is 4 (quadrupole moment).

    ζ  This point group is non-Abelian (some symmetry operations are not commutative).
       Therefore, the character table contains multi-membered classes and degenerate irreducible representations.

    η  The point group is chiral, as it does not contain any mirroring operation.

    θ  Some of the characters in the table are irrational because the order of the principal axis is neither 1,2,3,4 nor 6.
       These irrational values can be expressed as cosine values, or as solutions of algebraic equations with a leading coefficient of 1.
       All characters are algebraic integers of a degree just less than half the order of the principal axis.

    ι  The point group corresponds to a polygon inconstructible by the classical means of ruler and compass. Yet it becomes constructible
       if angle trisection is allowed, e.g., with neusis construction or origami. This is because the order of the principal axis is given
       by a product of any number of different Pierpont primes (...,5,7,13,17,19,37,73,97,109,163,...) times arbitrary powers of two and three.

    κ  The regular heptagon is the lowest regular polygon that cannot be constructed by compass and ruler alone, which has mystified
       mathematicians since antiquity. The reason for the inconstructibility of the heptagon is that cos(2π/7) has an algebraic degree of 3 and
       thus can not be represented by square roots and integer numbers. An algebraic representation becomes possible if cubic roots and complex numbers
       are used: 2*cos(2π/7) = (3√28+i*84*√3 + 3√28−i*84*√3 − 2)/6. This complex expression for a real value is hardly useful.