Real roots of the polynomials f_k(x)
The roots are computed using Pari/GP, 200 digits float precision
1) There is always one special root r_0. This approximates (k+1)/log(2)+1/2, and thus should never be integer
   see the computation in the column check. It is (r_0-1/2)*log(2) +1. The approximation is very fast.
2) The various other real roots seem to converge to integer and half-integer values. If they dont cross an integer while approximation
    they can never be integer
3) There are some inconsistencies(?, see the pink marker), where roots were expected by the (mod 4)-rhythm.
   Possibly these are incorrect approximations by float-point-calculation. Thus also the complex-roots should be cross-checked
                                           
  Polynomials f_k(x) , k== 1 (mod 4)                                
K= various roots r_1 to r_(k/4)                           r_0 Check r_0
1 roots(f1(x)= 1.0000 1.3466
5 roots(f5(x)= -1.2220 -1 6.2712 5.0003
9 roots(f9(x)= -1.4287 -1 12.0418 9.0002
13 roots(f13(x)= -1.4982 -1 -0.4990 -0.2351 17.8125 13.0001
17 roots(f17(x)= -1.5000 -1 -0.5000 -0.0566 23.5833 17.0001
21 roots(f21(x)= -2.2030 -2.0041 -1.5 -1 -0.5 -0.0018 29.3540 21.0001
25 roots(f25(x)= -2.4088 -2.0000 -1.5 -1 -0.5 0.0000 35.1248 25.0001
29 roots(f29(x)= -2.4944 -2.0000 -1.5 -1 -0.5 0.0000 0.5033 0.7254 40.8956 29.0001
33 roots(f33(x)= -2.4999 -2 -1.5 -1 -0.5 0.0000 0.5000 0.9199 46.6663 33.0001
37 roots(f37(x)= -3.1458 -3.0126 -2.5000 -2 -1.5 -1 -0.5 0.0000 0.5000 0.9954 52.4371 37.0000
41 roots(f41(x)= -3.3759 -3.0001 -2.5 -2 -1.5 -1 -0.5 0.0000 0.5 0.9999 58.2079 41.0000
45 roots(f45(x)= -3.4872 -3.0000 -2.5 -2 -1.5 -1 -0.5 0.0000 0.5 1.0000 1.5095 1.6671 63.9786 45.0000
49 roots(f49(x)= -3.4998 -3 -2.5 -2 -1.5 -1 -0.5 0.0000 0.5 1 1.5001 1.8867 69.7494 49.0000
53 roots(f53(x)=   -3.5000 -3 -2.5 -2 -1.5 -1 -0.5 0.0000 0.5 1 1.5000 1.9893 75.5202 53.0000
57 roots(f57(x)= -4.3347 -4.0004 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0.0000 0.5 1 1.5 1.9998 81.2910 57.0000
61 roots(f61(x)= -4.4737 -4.0000 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0.0000 0.5 1 1.5 2.0000 2.5446 2.5709 87.0617 61.0000
 
                                           
  Polynomials f_k(x) , k== 2 (mod 4)                                
K= various roots r_1 to r_(k/4)                           r_0 Check r_0
2 roots(f2(x)= -1 2.0000 2.0397
6 roots(f6(x)= -1.3058 -1 -1 7.7139 6.0003
10 roots(f10(x)= -1.5774 -1 -1 13.4845 10.0002
14 roots(f14(x)= -1.7736 -1 -1 19.2552 14.0001
18 roots(f18(x)= -1.9141 -1 -1 25.0260 18.0001
22 roots(f22(x)= -2.2741 -2.0245 -1.9840 -1 -1 30.7967 22.0001
26 roots(f26(x)= -2.5460 -2.0014 -1.9987 -1 -1 36.5675 26.0001
30 roots(f30(x)= -2.7453 -2.0001 -1.9999 -1 -1 42.3382 30.0001
34 roots(f34(x)= -2.8925 -2.0000 -2.0000 -1 -1 48.1090 34.0001
38 roots(f38(x)= -3.1936 -3.0543 -2.9741 -2.0000 -2.0000 -1 -1 53.8798 38.0000
42 roots(f42(x)= -3.4981 -3.0035 -2.9968 -2 -2 -1 -1 59.6506 42.0000
46 roots(f46(x)= -3.7072 -3.0003 -2.9997 -2 -2 -1 -1 65.4213 46.0000
50 roots(f50(x)= -3.8654 -3.0000 -3.0000 -2 -2 -1 -1 71.1921 50.0000
54 roots(f54(x)=   -3.9616 -3.0000 -3.0000 -2 -2 -1 -1 76.9629 54.0000
58 roots(f58(x)= -4.4422 -4.0066 -3.9941 -3.0000 -3.0000 -2 -2 -1 -1 82.7337 58.0000
62 roots(f62(x)= -4.6637 -4.0006 -3.9994 -3 -3 -2 -2 -1 -1 88.5044 62.0000
 
                                           
  Polynomials f_k(x) , k== 3 (mod 4)                                
K= various roots r_1 to r_(k/4)                           r_0 Check r_0
3 roots(f3(x)= -1 -0.8860 3.3860 3.0004
7 roots(f7(x)= -1 -0.6279 9.1565 7.0002
11 roots(f11(x)= -1 -0.5105 14.9272 11.0002
15 roots(f15(x)= -1.835 -1.500 -1 -0.5001 20.6979 15.0001
19 roots(f19(x)= -1.976 -1.500 -1 -0.5000 0.0327 0.0891 26.4686 19.0001
23 roots(f23(x)= -2.000 -1.5 -1 -0.5 0.0002 0.3538 32.2394 23.0001
27 roots(f27(x)= -2.000 -1.5 -1 -0.5 7E-07 0.4809 38.0102 27.0001
31 roots(f31(x)= -2.8000 -2.5006 -2 -1.5 -1 -0.5 2E-09 0.4997 43.7809 31.0001
35 roots(f35(x)= -2.9596 -2.5000 -2 -1.5 -1 -0.5 2E-12 0.5000   49.5517 35.0001
39 roots(f39(x)= -2.9989 -2.5 -2 -1.5 -1 -0.5 2E-15 0.5000 1.0006 1.3150 55.3225 39.0000
43 roots(f43(x)= -3.0000 -2.5 -2 -1.5 -1 -0.5 1E-18 0.5 1.0000 1.4655 61.0933 43.0000
47 roots(f47(x)= -3.7523 -3.5020 -3.0000 -2.5 -2 -1.5 -1 -0.5 5E-22 0.5 1 1.4991 66.8640 47.0000
51 roots(f51(x)= -3.9346 -3.5000 -3 -2.5 -2 -1.5 -1 -0.5 1E-25 0.5 1 1.5000   72.6348 51.0000
55 roots(f55(x)= -3.9970 -3.5000 -3 -2.5 -2 -1.5 -1 -0.5 3E-29 0.5 1 1.5000 2.0016 2.2667 78.4056 55.0000
59 roots(f59(x)= -4.0000 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 4E-33 0.5 1 1.5 2.0000 2.4418 84.1764 59.0000
63 roots(f63(x)= -4.6940 -4.5058 -4.0000 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 5E-37 0.5 1 1.5 2.0000 2.4975 89.9471 63.0000
 
                                           
  Polynomials f_k(x) , k== 0 (mod 4)                                
K= various roots r_1 to r_(k/4)                           r_0 Check r_0
4 roots(f4(x)= -1 -1 -0.8284 4.8284 4.0002
8 roots(f8(x)= -1 -1 -0.4957 10.5992 8.0002
12 roots(f12(x)= -1 -1 -0.2836 16.3699 12.0001
16 roots(f16(x)= -1 -1 -0.1262 22.1406 16.0001
20 roots(f20(x)= -1 -1 -0.0321   27.9113 20.0001
24 roots(f24(x)= -1 -1 -0.0036 0.0039 0.4709 33.6821 24.0001
28 roots(f28(x)= -1 -1 -0.0002 0.0002 0.6868 39.4529 28.0001
32 roots(f32(x)= -1 -1 -1E-05 1E-05 0.8506 45.2236 32.0001
36 roots(f36(x)= -1 -1 -4E-07 4E-07 0.9546   50.9944 36.0001
40 roots(f40(x)= -1 -1 -1E-08 1E-08 0.9929 1.008 1.4181 56.7652 40.0000
44 roots(f44(x)= -1 -1 -2E-10 2E-10 0.9993 1.001 1.6457 62.5359 44.0000
48 roots(f48(x)= -1 -1 -4E-12 4E-12 0.9999 1.000 1.8199 68.3067 48.0000
52 roots(f52(x)= -1 -1 -7E-14 7E-14 1.0000 1.000 1.9375   74.0775 52.0000
56 roots(f56(x)= -1 -1 -1E-15 1E-15 1.0000 1.000 1.9882 2.0151 2.3552 79.8483 56.0000
60 roots(f60(x)= -1 -1 -1E-17 1E-17 1.0000 1 1.9986 2.0014 2.5985 85.6191 60.0000