the Holmes child fight cleverestMycroft ask Sherlock Eurus find value fn f11 n2 fn number distinct order positive integer pair xy satisfy xyn gcdxy1 the integer gcdab great common divisor bSherlock say solve child play ask Mycroft instead value Summation positive integer d divide nEurus quietly observe finally come problem astonish Sherlock MycroftShe define kcomposite function Fkn recursively followsshe want tell value Fkn modulo 1000000007