1729 (number)

← 1728 1729 1730 →
Cardinalone thousand seven hundred twenty-nine
Ordinal1729th
(one thousand seven hundred twenty-ninth)
Factorization7 × 13 × 19
Divisors1, 7, 13, 19, 91, 133, 247, 1729
Greek numeral,ΑΨΚΘ´
Roman numeralMDCCXXIX, mdccxxix
Binary110110000012
Ternary21010013
Senary120016
Octal33018
Duodecimal100112
Hexadecimal6C116

1729 is the natural number following 1728 and preceding 1730. It is the first nontrivial taxicab number, expressed as the sum of two cubic positive integers in two different ways. It is known as the Ramanujan number or Hardy–Ramanujan number after G. H. Hardy and Srinivasa Ramanujan.

In mathematics

1729 is a composite number, the first nontrivial taxicab number, and a Carmichael number.[1] It is also the smallest absolute Euler pseudoprime.

1729 is the dimension of the Fourier transform on which the fastest known algorithm for multiplying two numbers is based.[2] This is an example of a galactic algorithm.[3]

1729 can be expressed as the quadratic form. Investigating pairs of its distinct integer-valued that represent every integer the same number of times, Schiemann found that such quadratic forms must be in four or more variables, and the least possible discriminant of a four-variable pair is 1729.[4]

1729 is the first number in the sequence of "Fermat near misses" defined, in reference to Fermat's Last Theorem, as numbers of the form which are also expressible as the sum of two other cubes.[5][6]

Ramanujan number

Main article: Taxicab number
1729 can be expressed as a sum of two positive cubes in two ways, illustrated geometrically.

1729 is also known as Ramanujan number or Hardy–Ramanujan number, named after an anecdote of the British mathematician G. H. Hardy when he visited Indian mathematician Srinivasa Ramanujan who was ill in hospital.[7][8] In their conversation, Hardy stated that the number 1729 from a taxicab he rode was a "dull" number and "hopefully it is not unfavourable omen", but Ramanujan remarked that "it is a very interesting number; it is the smallest number expressible as the sum of two cubes in two different ways".[9] This conversation led to the definition of the taxicab number as the smallest integer that can be expressed as a sum of two positive cubes in a given number of distinct ways. 1729 is the second taxicab number, expressed as and .[8]

1729 was later found in one of Ramanujan's notebooks dated years before the incident, and it was noted by French mathematician Frénicle de Bessy in 1657.[10] A commemorative plaque now appears at the site of the Ramanujan–Hardy incident, at 2 Colinette Road in Putney.[11]

See also

References

  1. ^ Koshy, Thomas (2007). Elementary Number Theory with Applications (2nd ed.). Academic Press. p. 340. ISBN 978-0-12-372487-8.
  2. ^ Harvey, David. "We've found a quicker way to multiply really big numbers". phys.org. Retrieved 2021-11-01.
  3. ^ Harvey, David; Hoeven, Joris van der (March 2019). "Integer multiplication in time ". HAL. hal-02070778.
  4. ^ Guy, Richard K. (2004). Unsolved Problems in Number Theory. Problem Books in Mathematics, Volume 1. Vol. 1 (3rd ed.). Springer. doi:10.1007/978-0-387-26677-0. ISBN 0-387-20860-7.
    ISBN 978-0-387-26677-0 (eBook)
  5. ^ Ono, Ken; Aczel, Amir D. (2016). My Search for Ramanujan: How I Learned to Count. p. 228. doi:10.1007/978-3-319-25568-2. ISBN 978-3-319-25568-2.
  6. ^ Sloane, N. J. A. (ed.). "Sequence A050794 (Consider the Diophantine equation () or 'Fermat near misses')". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  7. ^ Edward, Graham; Ward, Thomas (2005). An Introduction to Number Theory. Springer. p. 117. ISBN 978-1-85233-917-3.
  8. ^ a b Lozano-Robledo, Álvaro (2019). Number Theory and Geometry: An Introduction to Arithmetic Geometry. American Mathematical Society. p. 413. ISBN 978-1-4704-5016-8.
  9. ^ Hardy, G. H. (1940). Ramanujan. New York: Cambridge University Press. p. 12. I remember once going to see him when he was ill at Putney. I had ridden in taxi cab No. 1729 and remarked that the number seemed to me rather a dull one, and that I hoped it was not an unfavourable omen. "No," he replied, "it is a very interesting number; it is the smallest number expressible as the sum of two cubes in two different ways."
  10. ^ Kahle, Reinhard (2018). "Structure and Structures". In Piazza, Mario; Pulcini, Gabriele (eds.). Truth, Existence and Explanation: FilMat 2016 Studies in the Philosophy of Mathematics. Boston Studies in the Philosophy and History of Science. Vol. 334. p. 115. doi:10.1007/978-3-319-93342-9. ISBN 978-3-319-93342-9.
  11. ^ Marshall, Michael (24 February 2017). "A black plaque for Ramanujan, Hardy and 1,729". Good Thinking. Retrieved 7 March 2019.
allikas: https://en.wikipedia.org/wiki/1,729