isabelle/valid/mathd_numbertheory_211.thy (11 lines of code) (raw):

(* Authors: Wenda Li *) theory mathd_numbertheory_211 imports Complex_Main "HOL-Computational_Algebra.Computational_Algebra" "HOL-Number_Theory.Number_Theory" begin theorem mathd_numbertheory_211 : "card {n::nat. n<60 \<and> 6 dvd (4 * n - 2)} = 20" sorry end