Trekanttal: Forskelle mellem versioner

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'''Trekanttal''' er [[tal]], der indgår i talfølgen [[1 (tal)|1]], [[3 (tal)|3]], [[6 (tal)|6]], [[10 (tal)|10]], [[15 (tal)|15]], [[21 (tal)|21]], [[28 (tal)|28]], [[36 (tal)|36]], [[45 (tal)|45]], [[55 (tal)|55]], [[66 (tal)|66]], [[78 (tal)|78]], [[91 (tal)|91]], [[105 (tal)|105]], [[120 (tal)|120]] ... - altså således at det første trekanttal er 1, det andet er 1+2, det tredje er 1+2+3 og så videre.