New breakthrough in understanding (numerically) the MRB constant

Here is my latest attempt to find a super-fast method of computing the MRB constat as of 11/18/2014. (I still have a ways to go.) See Try to beat these MRB constant records! for my attempts at computing it. The notebook is attached so you can copy and edit it.

Reconstruct and greatly expand the above RootApproximant's (here f) and find they are approximated well by certain
 ((1+Sqrt[2])^n+(1-Sqrt[2])^n)/2.

Clear[key, f]

Block[{$MaxExtraPrecision = 1000}, For[x = 1, x <= 48,
        key[x] = Table[Convergents[Sqrt[2], 100][[2 n]], {n, 50}][[-x]];
        f[x] = Numerator[key[x]] - Denominator[key[x]] Sqrt[2];              
  Print[N[((1 + Sqrt[2])^n + (1 - Sqrt[2])^n)/2 /. n -> 100 + 2 (x - 1), 
     120 + x] - N[f[x], 120 + x]*ChebyshevT[100, 3]];
  x++]]


2.6387695903457195648070395905136485002528815*10^-39

4.527412857479332018505153596026307976091567*10^-40

7.767812414187964629605256710213628540205842*10^-41

1.332745910334467592580004301018691480319384*10^-41

2.28663047818840925874769095898520341710461*10^-42

3.9232376578577962668610274372430569943380*10^-43

6.7312116526268501368925503360630779498198*10^-44

1.1548933371831381527450276439478977555385*10^-44

1.981483704719787795776155276243085834114*10^-45

3.39968856487345247206655217979537449296*10^-46

5.83294342042836874637760316341388616634*10^-47

1.00077487383568775760009718252957206843*10^-47

1.7170582258575779922297993176354624423*10^-48

2.946006167885903773778240805170539698*10^-49

5.054547487396427203714516546686137636*10^-50

8.67223245519525484504691228411428839*10^-51

1.48791985720725703313630823782435395*10^-51

2.5528668804828735377093714283183531*10^-52

4.380027108246708948931461916665789*10^-53

7.514938446515183164950572168112005*10^-54

1.289359596624009500388813842014146*10^-54

2.21219133228873837382310883972869*10^-55

3.7955202749233523905051461823070*10^-56

6.5120832665273060479978869655528*10^-57

1.1172968499303123829358599702467*10^-57

1.916978330545682496172728559273*10^-58

3.28901483970971147677771653172*10^-59

5.64305732801443898939013597563*10^-60

9.6819557098951916856365053661*10^-61

1.6611609792267602199176724406*10^-61

2.850101654653696338695292773*10^-62

4.89000135654575832995032232*10^-63

8.38991592737586592749006203*10^-64

1.43948199879761226543714897*10^-64

2.4697606540980766513283182*10^-65

4.237439366123372535984192*10^-66

7.270296557594687026219692*10^-67

1.247385684334396797476231*10^-67

2.14017548411693758637696*10^-68

3.6719606135765754349947*10^-69

6.3000884029007674619849*10^-70

1.0809242816388504219628*10^-70

1.854572869323350697919*10^-71

3.18194399551599967885*10^-72

5.45935279862491093918*10^-73

9.3667683658946884656*10^-74

1.6070822091190214020*10^-74

2.757248888194399464*10^-75
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