ACR TAXIES ONTO ACTIVE WITHOUT CLRNC.

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I TAXIED ONTO THE ACTIVE RWY BELIEVING WE HAD A CLRNC FOR TKOF. I ASKED THE FO TO CONFIRM THAT CLRNC AND WAS INFORMED THAT IT WAS THE FIRST CONTACT WITH THE TWR AND WE WERE CLRED FOR TKOF. CONTRIBUTING FACTORS: 1) TIRED CREW (MIN LAYOVER) 2) EARLY DEP. 3) FMS NEEDED REPROGRAMMING DURING TAXI (A DISTRACTING SITUATION). 4) EXTRANEOUS COCKPIT CONVERSATION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES FLT WAS CLRED TO TAXI TO RWY 5 WHICH INDICATED CLRNC TO INTERSECTING RWY. HOWEVER; THE FMS DUMPED SOME FLT INFO AND CREW DISTRACTED TRYING TO REPROGRAM. WHEN CAME TO INTERSECTING RWY; CAPT ASKED FO TO GET CONFIRMATION FOR XING. WHEN ARRIVING AT ACTIVE RWY CAPT REALLY THOUGHT CLRNC WAS CLRNC FOR TKOF. ATTRIBUTES PROBLEM TO FATIGUE AS HOTEL WAS POOR AND SO WAS THE QUALITY OF SLEEP. BOTH PLTS CLRED FINAL BEFORE RWY ENTRY. GND CTLR WAS ALSO CLRNC DELIVERY AND POSSIBLY LCL AS WELL. NEVER RECEIVED INSTRUCTIONS TO SWITCH FROM GND TO TWR SO DID ON THEIR OWN JUST PRIOR TO CONTACTING AS TAXI ONTO RWY. NO OTHER MOVING TFC ON THE ARPT AT THAT TIME.