Question: Ten little Niggers, in American reprints and adaptations were all retitled "And Then There Were None", after the last five words in the nursery rhyme that has a roud folk song index number of what?

Context paragraphs:
Did You Ever See a Lassie?: "Did You Ever See a Lassie?"  is a folk song, nursery rhyme, and singing game.  It has a Roud Folk Song Index number of 5040.

Three Little Kittens: "Three Little Kittens" is an English language nursery rhyme, probably with roots in the British folk tradition.  The rhyme as published today however is a sophisticated piece usually attributed to American poet Eliza Lee Cabot Follen (1787–1860).  With the passage of time, the poem has been absorbed into the "Mother Goose" collection.  The rhyme tells of three kittens who first lose, then find and soil, their mittens.  When all is finally set to rights, the kittens receive their mother's approval and some pie.  It has a Roud Folk Song Index number of 16150.

A Wise Old Owl: "A Wise Old Owl" is an English language nursery rhyme.  It has a Roud Folk Song Index number of 7734 and in The Oxford Dictionary of Nursery Rhymes, 2nd Ed.  of 1997, as number 394.  The rhyme is an improvement of a traditional nursery rhyme "There was an owl lived in an oak, wisky, wasky, weedle."

Pretty Little Dutch Girl: "Pretty Little Dutch Girl" is a children's nursery rhyme, clapping game and jump-rope rhyme.  It has a Roud Folk Song Index number of 12986.

Ten Little Indians: Ten Little Indians is an American children's rhyme.  It has a Roud Folk Song Index number of 13512.  The word Indian usually refers to Native Americans.  The song is traditionally performed in the tune of the Irish folk song "Michael Finnegan".

Billy Boy: "Billy Boy" is a traditional folk song and nursery rhyme found in the United States.  It has a Roud Folk Song Index number of 326.  It is a variant of the traditional English folk song "My Boy Billy", collected by Ralph Vaughan Williams and published by him in 1912 as number 232 in "Novello's School Songs".  The song is very popular with the Orange Order.

And Then There Were None: And Then There Were None is a mystery novel by English writer Agatha Christie, widely considered her masterpiece and described by her as the most difficult of her books to write.  It was first published in the United Kingdom by the Collins Crime Club on 6 November 1939, as Ten Little Niggers, after the British blackface song, which serves as a major plot point.  The US edition was not released until December 1939; its American reprints and adaptations were all retitled "And Then There Were None", after the last five words in the nursery rhyme "Ten Little Indians".

Aiken Drum: "Aiken Drum" is a popular Scottish folk song and nursery rhyme, which probably has its origins in a Jacobite song about the Battle of Sheriffmuir (1715).  It has a Roud Folk Song Index number of 2571.

Tweedledum and Tweedledee: Tweedledum and Tweedledee are fictional characters in an English nursery rhyme and in Lewis Carroll's "Through the Looking-Glass, and What Alice Found There".  Their names may have originally come from an epigram written by poet John Byrom .  The nursery rhyme has a Roud Folk Song Index number of 19800.  The names have since become synonymous in western popular culture slang for any two people who look and act in identical ways, generally in a derogatory context.

Row, Row, Row Your Boat: "Row, Row, Row Your Boat" is an English language nursery rhyme and a popular children's song.  It can also be an "action" nursery rhyme, whose singers sit opposite one another and "row" forwards and backwards with joined hands.  It has a Roud Folk Song Index number of 19236.

Supporting paragraphs: And Then There Were None Ten Little Indians
Answer: 13512