The AGRA series of summer schools (Santiago de Chile, 2012; Cusco, 2015; Córdoba, 2018; Online, 2021) has as its goal to foster the development of number theory in Latin America: it provides a formative experience for young researchers, and it also helps bring together more senior or mid-career mathematicians working in the field. It has been our tradition to have all courses and associated discussions in Spanish or Portuguese, in part so as to make all activities accessible to all students in Latin America, regardless of their English proficiency.

The target audience of AGRA includes undergraduate students, graduate students and young researchers with a serious interest in number theory and neighboring fields. Due to the pandemic situation, AGRA IV was divided in two instalments. The first one was an ICTP – IMPA Online School that took place on August 16 – 20, 2021, with four minicourses covering topics in arithmetic combinatorics, arithmetic geometry, square-tiled surfaces and algebraic number theory (see http://indico.ictp.it/event/9617/). The plan for this second instalment, which shall happen in hybrid mode in the state of Rio de Janeiro – Brazil, is to have another group of minicourses, followed by tutorials and problem sessions.

Minicourses will be as follows:

Minicourse 1:
Interactions between ergodic theory and number theory
• Joel Moreira (Warwick, UK)
• Sebastián Donoso (Univ. de Chile)
 
Minicourse 2:
Applications of homology and cohomology in group theory
• Lev Glebsky (Universidad Autonoma de San Luis Potosi, Mexico)
• Dessislava Kochloukova (Unicamp, Brazil)
 
Minicourse 3:
Expansion, divisibility and parity: a walk on numbers and graphs
• Harald Helfgott (Univ. Göttingen, Germany/ CNRS, France)
• Adrián Ubis (UAM, Spain)
 
Minicourse 4:
Arithmetic groups and homogenous dynamics
• Sebastian Hurtado-Salazar (Univ. Chicago, USA)
• Plinio Pino (UFF, Brazil)

Minicourse 5:
Mori dream surfaces
• Michela Artebani (Univ. de Concepción, Chile)
• Antonio Laface (Univ. de Concepción, Chile)