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