La ecuación de Pell en las olimpiadas de matemáticas. Tzaloa: Revista de la Olimpiada Mexicana de Matemáticas (2022), no. 3, pp. 1-25.
Solving problems by looking at a discriminant. Mathematical Reflections (2020), no. 4, pp. 1-10.
With M. Z. Garaev & C. A. Díaz: Product of subsets of small intervals and points on exponential curves modulo a prime. Acta Arith. 193 (2020), no. 3, pp. 309-319.
The group-theoretic analog of Kuratowski's closure-complement theorem. Amer. Math. Monthly 126 (June-July 2019), no. 6, pp. 519-526, MR3956309.
With M. Z. Garaev: A note on $n!$ modulo $p$. Monatsh. Math. 182 (January 2017), no. 1, pp. 23-31, MR3592116.
With M.-C. Chang, J. Cilleruelo, M. Z. Garaev, I. E. Shparlinski, & A. Zumalacárregui: Points on curves in small boxes and applications. Michigan Math. J. 63 (2014), no. 3, pp. 503-534, MR3255689.
Sobre las series de los recíprocos de los números poligonales. Misc. Matemática (Octubre de 2012), núm. 55, págs. 1-11, MR3100379.

• With Daniel López-Aguayo & Leonardo Martínez-Sandoval: Un baúl de problemas olvidado (published electronically in universo.math): parte I, parte II, parte III, parte IV, parte V, parte VI


• On prime numbers represented by forms with a discriminant whose class number is one.

Varia invención

— Some manuscripts: Solutions to problems in Mathematical Reflections.

Mehr Lösungen.

— My sequences in the OEIS: A269665, A270441, A273217, A295866, A295868, A299028, A299030, A347933

— Answers to Prof. David E. Rowe's quiz on Gauss and Gaussian legends: they appeared in the pages of The Mathematical Intelligencer in 2016. Prof. Rowe was very kind to mention the answers that I sent to him in May 2016.

— On May 20 (2013), I sent a message to the editor of the Amer. Math. Monthly: it made it to the Editor's Endnotes of that year.

— A letter to the editor of Mathematical Reflections.

NEW! (Jan. 9th, 2023) Resources for the Olympiads (in Spanish).

Favorite sites


profile for J. H. S. at MathOverflow, Q&A for professional mathematicians

Apuntes Misceláneos (my blog)   • Collected papers of Paul Erdös   • El i$\pi$acional   •

  • Finding the class number of a neg. disc.   • Kuratowski's Closure-Complement Cornucopia

  • The Kurt Mahler Archive   • Number Theory Web   • NU Problem-Solving Group   • Ponder This!

Additional links



A reward check I received from Prof. Donald Knuth a few years ago.

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Last updated on Dec. 13th, 2022