úÎ0 d    !Copyright (c) 2018 Vanessa McHaleNoneb\( !n \). See -http://mathworld.wolfram.com/Derangement.htmlhereThe n.th Catalan number, with indexing beginning at 0. See  /http://mathworld.wolfram.com/CatalanNumber.htmlhere. 8»:> catalan <$> [0..9] [1,1,2,5,14,42,132,429,1430,4862] \binom{n}{k} See  1http://mathworld.wolfram.com/DoubleFactorial.htmlhere.Safe !Copyright (c) 2018 Vanessa McHaleNoneÄ O(\sqrt(n)) !Copyright (c) 2018 Vanessa McHaleNone ²See /http://mathworld.wolfram.com/PerfectNumber.htmlhereSum of proper divisors. Number of distinct divisors. Euler totient function.  Safe V See  -http://mathworld.wolfram.com/Derangement.htmlhere. V»:> fmap derangement [0..10] :: [Integer] [1,0,1,2,9,44,265,1854,14833,133496,1334961]       -fast-arithmetic-0.4.0.0-9IUtjkEB6MHGs6Qiv5RxpNumeric.CombinatoricsNumeric.IntegerNumeric.NumberTheory Numeric.PureNumeric.Common derangementcatalanchoose factorialdoubleFactorialisPrime isPerfect sumDivisors littleOmegatautotient hsDerangementasTest conjugate