Zhāng Qiūjiàn 張邱建
5th-century mathematician (Sui-period or slightly earlier per the Sìkù 提要 of KR3f0039 Zhāng Qiūjiàn suànjīng; some scholars place him in the Northern-Wèi). Native of Qīnghé 清河 (in modern Héběi), per his self-styled signature in the work’s preface. Birth and death years not securely recorded.
His sole surviving work is the Zhāng Qiūjiàn suànjīng 張邱建算經 (KR3f0039), in 3 juàn containing 100 problems-and-solutions of advanced mathematical character (notably more sophisticated than the elementary KR3f0033 Sūnzǐ and KR3f0036 Wǔcáo but less ambitious than the KR3f0032 Jiǔzhāng). The work is famous for the so-called Hundred Fowls problem (bǎijī wèntí 百雞問題) — a system of indeterminate equations (a chicken costs 5 qián, a hen 3 qián, three chicks 1 qián; with 100 qián purchase 100 fowls) — the foundational Chinese problem in indeterminate analysis, anticipating Diophantine analysis by centuries.
The work was canonized as one of the Suànjīng shíshū under the Tang Imperial Academy curriculum; annotated by 甄鸞 Zhēn Luán (Northern Zhōu), then re-annotated under imperial commission by 李淳風 Lǐ Chúnfēng (Tang, 656); a xìcǎo (detailed-procedural) elaboration was added by Liú Xiàosūn 劉孝孫 of the Tang Imperial Academy mathematics department. The Sìkù-preserved recension descends from the Northern-Sòng imperial-secretariat edition by Zhào Yànruò 趙彦若 (printed under Yuánfēng / Zhàoshèng era reign-titles, c. 1080).