“Book of Numbers” is a thematic and stylistic continuation of “Four New Messages,” Cohen’s story collection dealing with the vagaries of life in the Internet era. Readers of his previous work will recognize his antic, breakneck excesses; even his short stories overflow. Cohen makes no bones about his impatience with conventional narrative — he, or rather his fictional stand-in (also named Joshua Cohen), announces his disdain for the dusty tropes of the novel on the first page: “There’s nothing worse than description: hotel room prose. No, characterization is worse. No, dialogue is.” Unsurprisingly, on those counts, “Book of Numbers” is sometimes a hot mess.