We investigate sums of mixed powers involving two squares and three
biquadrates. In particular, subject to the truth of the Generalised Riemann
Hypothesis and the Elliott-Halberstam Conjecture, we show that all large
natural numbers n with 8 not dividing n, n not congruent to 2 modulo 3, and n
not congruent to 14 modulo 16, are the sum of 2 squares and 3 biquadrates.Comment: to appear in Mathematik
