It's all about the Pentha and the number 5. Penthatlon - Olympic sport that comprises 5 different events. Pentanol - alcohol with 5 carbon atoms. Pentane - a molecule with 5 carbon atoms. Pente / penta - Greek meaning 5 or 5th. https://translate.google.com/#view=home&op=translate&sl=el&tl=en&text=πέντε Penta cost / pentagon / pentagram meaning five or fifth.