import std.stdio, std.algorithm, std.range; int male(in int n) pure nothrow { return n ? n - male(n - 1).female : 0; } int female(in int n) pure nothrow { return n ? n - female(n - 1).male : 1; } void main() { 20.iota.map!female.writeln; 20.iota.map!male.writeln; }