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Claim. Every sufficiently large integer is the sum of at most three powerful numbers (integers $n$ such that $p\mid n$ implies $p^2\mid n$). This answers Problem 941 affirmatively. The result is D. R. Heath-Brown, Ternary quadratic forms and sums of three square-full numbers, Séminaire de Théorie des Nombres, Paris 1986–87, Progress in Mathematics 75, Birkhäuser Boston (1988), 137–163. Only the publication year is recorded, so the page is dated to the start of 1988. The question reached the Oberwolfach problem book in 1986 as a problem of Erdős and Ivić; the site also cites Erdős's 1976 Manitoba survey [Er76d].

Method. The title names the approach, ternary quadratic forms: a sum of three powerful numbers is a value of a form $a^3x^2+b^3y^2+c^3z^2$. No account of the paper's argument is recorded.

Acceptance. The site's curator, Thomas Bloom, marks Problem 941 proved and credits this paper for the proof. The volume is an edited seminar proceedings rather than a journal, so no refereed evidence is listed. No formal proof is on record; formal-conjectures states the result without proof, tagged research solved, as erdos_940.variants.three_powerful in 940.lean and erdos_1107.variants.two in 1107.lean. The generalization to $r$-powerful numbers with $r\ge3$ is Problem 1107; Problem 940 asks the analogous questions for sums of at most $r$ $r$-powerful numbers with $r\ge3$, and Problem 1081 concerns sums of two powerful numbers.

Depends on. No other wiki page; the claim rests on the cited paper.