"I Am a Rock" is a song written by Paul Simon.
 It was first performed by Simon alone as the opening track on his album "The Paul Simon Songbook" which he originally recorded and released in August 1965, only in the United Kingdom.
 Paul Simon and Art Garfunkel, as the American folk rock duo Simon and Garfunkel, re-recorded it on December 14, 1965, and included as the final track on their album "Sounds of Silence", which they released on January 17, 1966.
John E. Gatchell (November 27, 1945 — July 9, 2004) was an American jazz trumpeter who was prolific in New York City recording studios from the 1970s to the mid-1980s.
 After serving in the U.S. Navy in the late 1960s, Gatchell became one of the founding members of the horn band "Ten Wheel Drive," then "Gotham."
 Gatchell was among the musicians hand-selected by Paul Simon, who chose whom he considered to be the finest studio musicians for the 1981 "Simon & Garfunkel Concert in Central Park"
Paul Simon's Concert in the Park is a live album released in 1991 by Paul Simon.
 It provided a survey of his two most recent albums, "Graceland" and "Rhythm of the Saints", and also drew liberally from his earlier songbook including a number of tunes from the Simon and Garfunkel era.
 600,000 people were initially claimed to have attended the show, which was held in Central Park, New York City on August 15, 1991.
 Later estimates determined that the maximum number of people who could fit in the park space was 48,500.
 The concert was similar to The Concert in Central Park, a reunion concert for Simon and Garfunkel held ten years earlier.
 The album was released on the 50th birthday of Art Garfunkel.
Paul Simon is the second studio album by American singer-songwriter Paul Simon as a solo artist.
 It was released in January 1972, nearly two years after he split up with longtime musical partner Art Garfunkel.
 His first solo album was recorded in England in 1965 but remained unreleased in the U.S. (except for a brief period in 1969) until 1981, when it appeared in the 5-LP "Collected Works" boxed set.
 Originally released on Columbia Records, "Paul Simon" was then issued under the Warner Bros. label and is now back with Columbia through Sony.
 The album topped the charts in the United Kingdom, Japan and Norway and reached No. 4 on the U.S. Billboard Pop Albums.
 In 1986 it was certified platinum.
The Concert in Central Park, released in February 1982 on Warner Bros.
 Records, is the first live album by American folk rock duo Simon & Garfunkel.
 It was recorded in September 1981 at a free benefit concert in Central Park, New York City, where the pair performed in front of more than 500,000 people.
 Proceeds went toward the redevelopment and maintenance of the park, which had deteriorated due to lack of municipal funding.
 The concert and album marked the start of a short-lived reunion for Paul Simon and Art Garfunkel.
Paul Simon in Concert: Live Rhymin' is an album by Paul Simon, released in March 1974 by Columbia Records.
 It was recorded in the wake of the release of "There Goes Rhymin' Simon – which produced a number of hit singles ("Kodachrome" and "Loves Me Like a Rock") and radio staples (as "Something So Right" and "Take Me to the Mardi Gras") during Simon's 1973-74 tour, at Nassau Veterans Memorial Coliseum, New York, July 10th, 1973. "
 However, the album presents a very truncated version of the concerts he performed on this tour, which consisted of up to 24 songs.
 The album fails to note where the performances were recorded, although according to liner notes in a later Simon compilation, "Duncan" is from a London concert and "American Tune" was recorded in New York City.
The Paul Simon Songbook is the first solo studio album by Paul Simon.
 It was recorded in London and released in the UK in 1965 and was supposedly deleted in 1969 at Simon's request.
 It was made available in the U.S. as part of the LP box set "Paul Simon: Collected Works" (1981).
 The album was produced by Reginald Warburton and Stanley West as CBS Records LP 62579; remastered CD Columbia/Legacy 90281.
Recorded as Jerry Landis is a compilation album of music by singer, songwriter, and guitarist Paul Simon, released in 2006.
 This album contains 18 songs recorded before Simon & Garfunkel released their first album, "Wednesday Morning, 3 A.M.".
 All songs are by Paul Simon except the song "Beat Love", which is a contemporary recording by Art Garfunkel, recorded under the name "Artie Garr".
 This album was released six years after an album of Simon & Garfunkel songs, from the same era, that contained a mix of Simon & Garfunkel recordings (under the name "Tom & Jerry"), and Paul Simon and Art Garfunkel songs.
 He recorded many of the songs on these albums under different aliases, such as "Jerry Landis", "True Taylor" and "Paul Kane".
"So Long, Frank Lloyd Wright" is a song written by Paul Simon that was originally released on Simon & Garfunkel's 1970 album "Bridge over Troubled Water".
 It has since been released on several Simon & Garfunkel compilation albums.
 It has also been recorded by the London Pops Orchestra and Joe Chindamo trio.
 Art Garfunkel has stated that the origin of the song came from his request that Paul Simon write a song about the famous architect Frank Lloyd Wright while Simon has stated that he wrote the song, despite not knowing who Wright was.
 Garfunkel sings lead on the majority of the song while Simon sings on the bridge.
Paul Simon 1964/1993 is a compilation album released in 1993 by Paul Simon.
 It contains a collection of recordings ranging from his earliest collaboration with Art Garfunkel (the 1957 release "Hey, Schoolgirl") and further Simon & Garfunkel hits to songs from his subsequent solo career.
 Despite carrying the title "Paul Simon 1964/1993", the music on this compilation was recorded between 1957 and 1991, and no tracks were recorded in 1964 or 1993.

Question: The album in which John Gatchell collaborated with Paul Simon in 1981 was performed in front of how many people?
Answer: more than 500,000