Hi, I tried to report this bug to salesforce, but was redirected here.
This is very likely internal salesforce issue.
When you try to do any operation with integer received from lightning component (@AuraEnabled), you got 
FATAL_ERROR|Internal Salesforce.com Error
 

public with sharing class TestController2 {
    @AuraEnabled
    public static integer getTestResult(integer pageNumber) {
        return pageNumber + 1;
    }
}

Full log included:

34.0 APEX_CODE,DEBUG;APEX_PROFILING,INFO;CALLOUT,INFO;DB,INFO;SYSTEM,DEBUG;VALIDATION,INFO;VISUALFORCE,INFO;WORKFLOW,INFO
23:30:39.143 (143052245)|EXECUTION_STARTED
23:30:39.143 (143081946)|CODE_UNIT_STARTED|[EXTERNAL]|01pU0000001YzfB|TestController2.getTestResult
23:30:39.143 (143501666)|METHOD_ENTRY|[1]|01pU0000001YzfB|TestController2.TestController2()
23:30:39.143 (143599706)|SYSTEM_MODE_ENTER|false
23:30:39.143 (143634027)|SYSTEM_MODE_EXIT|false
23:30:39.143 (143644512)|METHOD_EXIT|[1]|TestController2
23:30:39.144 (144047168)|FATAL_ERROR|Internal Salesforce.com Error
23:30:39.144 (144066440)|CUMULATIVE_LIMIT_USAGE
23:30:39.144 (144066440)|LIMIT_USAGE_FOR_NS|(default)|
  Number of SOQL queries: 0 out of 100
  Number of query rows: 0 out of 50000
  Number of SOSL queries: 0 out of 20
  Number of DML statements: 0 out of 150
  Number of DML rows: 0 out of 10000
  Maximum CPU time: 0 out of 10000
  Maximum heap size: 0 out of 6000000
  Number of callouts: 0 out of 100
  Number of Email Invocations: 0 out of 10
  Number of future calls: 0 out of 50
  Number of queueable jobs added to the queue: 0 out of 50
  Number of Mobile Apex push calls: 0 out of 10

23:30:39.144 (144066440)|LIMIT_USAGE_FOR_NS|Vendavo|
  Number of SOQL queries: 0 out of 100
  Number of query rows: 0 out of 50000
  Number of SOSL queries: 0 out of 20
  Number of DML statements: 0 out of 150
  Number of DML rows: 0 out of 10000
  Maximum CPU time: 0 out of 10000
  Maximum heap size: 0 out of 6000000
  Number of callouts: 0 out of 100
  Number of Email Invocations: 0 out of 10
  Number of future calls: 0 out of 50
  Number of queueable jobs added to the queue: 0 out of 50
  Number of Mobile Apex push calls: 0 out of 10

23:30:39.144 (144066440)|CUMULATIVE_LIMIT_USAGE_END

23:30:39.144 (144134140)|CODE_UNIT_FINISHED|TestController2.getTestResult
23:30:39.147 (147174875)|EXECUTION_FINISHED

Note that system.debug('pageNumber: ' + pageNumber); works. But all other integer operations fail.
Please advise how to circumvent this issue.