Are there any numbers greater than $26033514998417$ which can be expressed as a sum of two positive 4th powers in atleast 2 ways ?
And if there are any such numbers, then, please include the number(s) that u have found in your answer.
In case, if anybody wants to know how the number
$26033514998417$ can be expressed as a sum of two positive 4th powers in 2 ways, here it is: https://math.stackexchange.com/a/4237040/857041
$$17472238301875630082 = 62047^4 + 40351^4 = 59693^4 + 46747^4$$ from A018786, all primes btw.
Dunno why that list stops at 835279626752, though, presumably because a sequence must be complete, i.e. all numbers smaller and not in the list must not have the property.
Addendum: and here is a list with 516 primitive entries from Daniel J. Bernstein (found via A003824), that ends
Addendum 2: Here is a 146-digit solution from PrimePuzzles 103
They mention an identity from a collection by Edward Brisse on EulerNet: $$f_2^4(a,b)+f_2^4(b,-a)=f_2^4(a,-b)+f_2^4(b,a)$$ where $$f_2(a,b)= -a^{13}+a^{12}b+a^{11}b^2+5a^{10}b^3+6a^9b^4-12a^8b^5-4a^7b^6+7a^6b^7-3a^5b^8-3a^4b^9+4a^3b^{10}+2a^2b^{11}-ab^{12}+b^{13}$$
The collection has also (other) identidies of degree 7, 13, 19 and 31 for $a$, $b$, $c$, $d$. And there are identities that solve $x^4+y^4+z^4=2w^4$ like
$$(a^2-b^2)^4 + (a^2 + 2ab)^4 + (2ab + b^2)^4 = 2(a^2 + ab + b^2)^4$$
So this rabbit hole seems to go infinitly deep, both in terms of formulae and in terms of solutions you can generate with each formula.