Question: One example of alliteration is the tongue-twister with 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.

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.

The Twelve Days of Christmas (song): "The Twelve Days of Christmas" (Roud 68) is an English Christmas carol that enumerates in the manner of a cumulative song a series of increasingly grand gifts given on each of the twelve days of Christmas (the twelve days that comprise the Christmas season starting with Christmas Day).  The song, published in England in 1780 without music as a chant or rhyme, is thought to be French in origin.  "The Twelve Days of Christmas" has a Roud Folk Song Index number of 68.  The tunes of collected versions vary.  The standard tune now associated with it is derived from a 1909 arrangement of a traditional folk melody by English composer Frederic Austin, who first introduced the now familiar prolongation of the verse "five gold rings".

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.

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".

Roud Folk Song Index: The Roud Folk Song Index is a database of nearly 200,000 references to nearly 25,000 songs that have been collected from oral tradition in the English language from all over the world.  It is compiled by Steve Roud, a former librarian in the London Borough of Croydon.  Roud's Index is a combination of the Broadside Index (printed sources before 1900) and a "field-recording index" compiled by Roud.  It subsumes all the previous well-known printed sources known to Francis James Child (the Child Ballads) and includes recordings from 1900 to 1975.  Until early 2006 the index was available only by a CD subscription; it can now be found online on a website maintained by the English Folk Dance and Song Society (EFDSS).  A partial list is also available at List of folk songs by Roud number.

Peter Piper: "Peter Piper" is an English-language nursery rhyme and well-known alliteration tongue-twister.  It has a Roud Folk Song Index number of 19745.

The Crabfish: "The Crabfish" is a ribald humorous folk song of the English oral tradition.  It dates back to the seventeenth century, appearing in Bishop Percy's Folio Manuscript as a song named "The Sea Crabb" based on an earlier tale.  It has a Roud Folk Song Index number of 149.  The moral of the story is that one should look in the chamber pot before using it.

Lavender's Blue: "Lavender's Blue" (sometimes called "Lavender Blue") is an English folk song and nursery rhyme dating to the 17th century.  It has a Roud Folk Song Index number of 3483.  It has been recorded in various forms since the 20th century and some pop versions have been hits in the US and UK charts.

Alliteration: Alliteration is a figure of speech and a stylistic literary device which is identified by the repeated sound of the first or second letter in a series of words, or the repetition of the same letter sounds in stressed syllables of a phrase.  "Alliteration" is from the Latin word "littera", meaning "letter of the alphabet", and the first known use of the word to refer to a literary device occurred around 1624.  Alliteration narrowly refers to the repetition of a letter in any syllables that, according to the poem's meter, are stressed, as in James Thomson's verse "Come…dragging the lazy languid Line along".  Another example is "Peter Piper picked a peck of pickled peppers".

Supporting paragraphs: Alliteration Peter Piper
Answer: 19745