素数でないことを証明するテクニック。二項係数と5の累乗の積で表された和

This is the 920th episode of Fukuda's Fun Math. A technique to prove that a number is not prime. A sum expressed as the product of a binomial coefficient and a power of 5. [Subscribe to the channel here]    / @tamoshop   [Fukuda's Math Webpage is here] http://www.tamoshop.com An index of currently released videos, comments on problems, Fukuda's app introductions, and the administrator's room also features haiku and essays about his hometown, Yaizu! [Twitter is here]   / fukudatamoshop   [Fukuda's Entrance Exam Problem Explanation App] Tokyo, Kyoto, Hokkaido, Tohoku, Tsukuba, Chiba, Hitotsubashi, Tokyo Institute of Technology, Tokyo Medical and Dental University, Hamamatsu University School of Medicine, Nagoya, Osaka, Kobe, Kyushu Includes entrance exam problems, solutions (still images), and explanations (videos) for all 14 universities from the past 7 years. How to obtain (Free, with in-app purchases... All data for the latest year is free) Download from the following sites: For iPhone and iPad (Apple App Store) https://apps.apple.com/app/%E7%A6%8F%... Android (Google (Play Store) https://play.google.com/store/apps/de... [App for Math Explanations for Entrance Exams of Famous Private Universities in the Tokyo Metropolitan Area] Waseda, Keio University, Aoyama Gakuin University, Sophia University, Meiji University, Rikkyo University, Chuo University, Tokyo Jikei University School of Medicine Includes entrance exam questions, answers (still images), and explanations (videos) for all 8 universities from the past 3 years. How to obtain (Free, with in-app purchases... All data for the latest year is free) Download from the following sites: iPhone (Apple App Store) https://apps.apple.com/app/%E7%A6%8F%... Android (Google (Play Store) https://play.google.com/store/apps/de... Other apps by Fukuda 【gDraw】Graph drawing gDraw for iPhone (250 yen) https://apps.apple.com/app/id689603480 gDrawLite (Limited features version) Free https://apps.apple.com/app/gdrawlite/... gDrawPro (for iPad) Free (In-app purchases available) https://apps.apple.com/app/id907360838 【Fractional Calculator】Fractional calculations, calculations including mixed numbers, answers in fractions (Free) iPhone, iPad (App Store) https://apps.apple.com/app/id998791093 Android (Google Play Store) https://play.google.com/store/apps/de... [Real Number Calculator] Square root calculation, rationalization freely, and answers remain as square roots (Free) iPhone, iPad (App Store) https://apps.apple.com/app/squareroot... [Function Calculator] Calculate the value of rational functions, and get results as fractions and rules (Free) iPhone, iPad (App Store) https://apps.apple.com/app/functionca... [Triple Calculator] A triple calculator. Super-fast calculations with three calculators switching between them (free) iPhone, iPad (App Store) https://apps.apple.com/app/triplecalc... Android (Google Play Store) https://play.google.com/store/apps/de... [Learn Multiplication Tables by Listening and Speaking] A multiplication table app that uses voice recognition for practice. Master multiplication tables by speaking them aloud! (Free with in-app purchases) iPhone, iPad (App Store) https://apps.apple.com/app/%E8%81%9E%... Android (Google Play Store) https://play.google.com/store/apps/de...