Recamán's triangular fibonacci
JavaScript (ES6), 164 163 148 bytes

Input format: F(n), R(n), T(n)

s=&gt;eval(s.replace(/[FRT]/g,c=&gt;`(F=n=&gt;${c&lt;'R'?'n&gt;1?F(n-2)+F(n-1):n':c&gt;'R'?'n*++n/2':'(N=&gt;{for(l=[1];--n;)l[x=y+=++N&gt;y|l[y-N]?N:-N]=1})(x=y=0)|x'})`))


Example

This may take a few seconds to complete.



let f =

s=&gt;eval(s.replace(/[FRT]/g,c=&gt;`(F=n=&gt;${c&lt;'R'?'n&gt;1?F(n-2)+F(n-1):n':c&gt;'R'?'n*++n/2':'(N=&gt;{for(l=[1];--n;)l[x=y+=++N&gt;y|l[y-N]?N:-N]=1})(x=y=0)|x'})`))

console.log(f("((R(1) + R(2)) + (R(57) - R(35))) / (R(51) - R(41)) + (F(30) + F(31)) - (T(53))"));