dapper - return a list of INT
I think that you should specify the type you expect from your query like below:
var ids = connection.Query<int>("storedprocedure",
param,
transaction: transaction,
commandType: CommandType.StoredProcedure);
You could check this Execute a query and map the results to a strongly typed List for further info.
This is very similar but with .ToList() as IList<int>
var ids = connection.Query<int>("storedprocedure",
param, transaction:transaction, commandType: CommandType.StoredProcedure)
.ToList() as IList<int>