{"description":"http://projecteuler.net/index.php?section=problems&id=44 \u307e\u305a\u3001\u3067\u304d\u308b\u3060\u3051\u6570\u5b66\u3092\u4f7f\u308f\u306a\u3044\u65b9\u6cd5\u3067\u66f8\u3044\u305f\u3002Pl\u3092l\u304c\u5c0f\u3055\u3044\u307b\u3046\u304b\u3089\u8abf\u3079\u3001Pk\u3068\u306e\u548c\u304c\u4e94\u89d2\u6570\u3067\u3042\u308b\u3082\u306e\u3092\u63a2\u3059\u3002\u305f\u3060\u3057\u3001k\u306fPk+1-Pk \u2264 Pl\u3092\u6e80\u305f\u3059\u9650\u308a\u3002\u305d\u306e\u4e2d\u3067Pl + 2Pk\u304c\u4e94\u89d2\u6570\u3067\u3042\u308b\u3082\u306e\u3092\u63a2\u3059\u3002\u304d\u308c\u3044\u306b\u66f8\u3051\u305f\u3002 int_sqrt :: Int -> Int int_sqrt n = floor (sqrt (fromIntegral n)) is_pentagonal n = m * m == k && mod (1 + m) 6 == 0 where k = 1 \u2026","blog_url":"https://inamori.hateblo.jp/","provider_name":"Hatena Blog","title":"Project Euler 44","height":"190","categories":["Haskell"],"image_url":null,"width":"100%","blog_title":"inamori\u2019s diary","html":"<iframe src=\"https://hatenablog-parts.com/embed?url=https%3A%2F%2Finamori.hateblo.jp%2Fentry%2F20100214%2Fp2\" title=\"Project Euler 44 - inamori\u2019s diary\" class=\"embed-card embed-blogcard\" scrolling=\"no\" frameborder=\"0\" style=\"display: block; width: 100%; height: 190px; max-width: 500px; margin: 10px 0px;\"></iframe>","version":"1.0","published":"2010-02-14 00:00:01","author_url":"https://blog.hatena.ne.jp/inamori/","author_name":"inamori","url":"https://inamori.hateblo.jp/entry/20100214/p2","type":"rich","provider_url":"https://hatena.blog"}