Question: How long did a series of 6 erotic feature films run after being ushered in by the 1965 Danish coming-of-age sex comedy;Sytten?

Context paragraphs:
It's Nifty in the Navy: It's Nifty in the Navy (Danish: "Flådens friske fyre" ) is a 1965 Danish comedy film directed by Finn Henriksen and starring Dirch Passer.

A Taste of Blood: A Taste of Blood is a 1967 American horror film, produced and directed by Herschell Gordon Lewis.  It stars, among others, Bill Rogers and Elizabeth Wilkinson.  The movie was also known as "The Secret of Dr. Alucard".  Lewis considered this his masterpiece, which may account for the film's relatively long running time of two hours (most of Lewis's films run no longer than 80 minutes).

Sytten: Sytten (English title: Erik Soya's 17) is a 1965 Danish coming-of-age sex comedy directed by Annelise Meineche and starring Ole Søltoft and Ghita Nørby.  Søltoft plays a 17-year-old high school student who discovers the youthful excesses of sexual desire during his summer vacation in 1913.  Based upon the semi-autobiographical 1953 novel by Carl Erik Soya, Sytten was a financial success for the Palladium Film company and ushered in a wave of erotic films such as the "Bedside"-films and "Zodiac"-films, most of which starred Søltoft.

The Girl and the Millionaire: The Girl and the Millionaire (Danish: "Pigen og millionæren" ) is a 1965 Danish comedy film directed by Ebbe Langberg and starring Dirch Passer.

Tree of Knowledge (film): Tree of Knowledge (Danish: Kundskabens træ ) is a 1981 Danish coming-of-age drama directed by Nils Malmros.  The film details the lives of 17 teenage schoolmates in 1950s Denmark.  Shooting on location at the high school which he had attended, Malmros took two years to film the action, so the cast members reflected the real life physical and emotional development of their characters.  Film Critic Roger Ebert of the Chicago Sun-Times wrote ""The Tree of Knowledge" is the truest and most moving film I have ever seen about the experience of puberty... a creative act of memory about exactly what it was like to be 13 in 1953."  Despite critical praise, "Tree of Knowledge" received only two awards: the Danish Film Critics Bodil Award for Jan Weincke's cinematography and the Audience Award at the Lübeck Nordic Film Festival.  "Tree of Knowledge" is one of the top 100 Danish films listed by the Danish Film Institute and is one of ten films listed in the cultural canon of Denmark by the Danish Ministry of Culture.

Innocent Pictures: Innocent Pictures ApS is a Danish independent film company founded in 2001, originally as a subsidiary of Lars von Trier's film company Zentropa, which is best known for the production of the erotic feature film "All About Anna" (2005), starring Gry Bay.

The Adventures of Justine: The Adventures of Justine is a series of seven erotic feature films and television films featuring Daneen Boone as the heroine Justine Wilkenson.

Zazel: Zazel: The Scent of Love (also known as "Zazel: Philip Mond's Scent of Love" and "ZTSOL") is a highly regarded award-winning American adult erotic film, photographed in October 1995 and released the following year.  "Zazel" is described as "a great angel, invoked in Solomonic magic, who is "effective in love conjurations"".  The film was produced by Cal Vista Studios—reportedly made at a cost of $237,000—and was directed by Dutch fashion photographer and filmmaker Philip Mond, who also did the camera work and designed the costumes and special make-up.  It was Mond's second adult erotic feature after "Sex Off the Runway"—and like his previous film, "Zazel" also featured a bevy of Penthouse Pets, including 1994 Pet of the Year, Sasha Vinni; 1995 Pet of the Year, Gina LaMarca; and 1999 Pet of the Year, Nikie St. Gilles.

Zodiac-films: The "Zodiac"-films is a series of six feature films from 1973–78, and form part of the wave of erotic films from Denmark.

Ole Søltoft: Ole Søltoft (8 January 1941 – 9 May 1999 in Kolding) was a Danish actor who became an icon of the 1970s wave of Danish erotic feature film comedies.  For over a decade he starred or co-starred in nearly all notable films in this genre and became hopelessly typecast, usually playing naive, likeable guys with a healthy sexual appetite.  He is especially remembered for the "Bedside"-films and "Zodiac"-films, though his big breakthrough was as the romantic lead in Annelise Meineche's "Sytten" (1965).

Supporting paragraphs: Sytten Zodiac-films
Answer: from 1973–78