The polynomial X²+Y⁴ captures its primes

This article proves that there are infinitely many primes of the form a^2 + b^4, in fact getting the asymptotic formula. The main result is that \sum_{a^2 + b^4\le x} \Lambda(a^2 + b^4) = 4\pi^{-1}\kappa x^{3/4} (1 + O(\log\log x / \log x)) where a, b run over positive integers and \kappa = \int^1_0 (1 - t^4)^{1/2} dt = \Gamma(1/4)^2 /6\sqrt{2\pi}. Here of course, \Lambda denotes the von Mangoldt function and \Gamma the Euler gamma function.