Numerical semigroups with concentration two Rosales González, José Carlos Numerical semigroup Concentration Frobenius number Genus Multiplicity Wilf's conjecture The first author was partially supported by MTM-2017-84890-P and by Junta de Andalucia group FQM-343. The second author is supported by the project FCT PTDC/MAT/73544/2006). 2010 Mathematics Subject Classification: 20M14, 11D07. We define the concentration of a numerical semigroup S as C(S) = max {next(S)(s) - s vertical bar s is an element of S\{0}} wherein next(S)(s) = min {x is an element of S vertical bar s < x}. In this paper, we study the class of numerical semigroups with concentration 2. We give algorithms to calculate the whole set of this class of semigroups with given multiplicity, genus or Frobenius number. Separately, we prove that this class of semigroups verifies the Wilf's conjecture. 2022-04-01T11:29:35Z 2022-04-01T11:29:35Z 2021-03-30 info:eu-repo/semantics/article Published version: José C. Rosales, M.B. Branco, Márcio A. Traesel, Numerical semigroups with concentration two, Indagationes Mathematicae, Volume 33, Issue 2, 2022, Pages 303-313, ISSN 0019-3577, [https://doi.org/10.1016/j.indag.2021.07.004] http://hdl.handle.net/10481/74054 eng http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España Elsevier